Starting from setuptools-dso 1.6 pyx.build no longer fails on macOS due to:

  https://github.com/mdavidsaver/setuptools_dso/commit/dd2cf303
  https://github.com/mdavidsaver/setuptools_dso/commit/6883d6dc
  https://github.com/mdavidsaver/setuptools_dso/commit/78ae8852
  https://github.com/mdavidsaver/setuptools_dso/pull/9
  https://github.com/mdavidsaver/setuptools_dso/issues/8

It was previously failing with setuptools-dso==1.5:

  (py3.venv) kirr@Kirills-iMac pygolang % python -m pytest
  ==================================== test session starts =====================================
  platform darwin -- Python 3.7.6, pytest-5.3.5, py-1.8.1, pluggy-0.13.1
  rootdir: /Users/kirr/pygolang
  collected 100 items

  golang/_gopath_test.py ..                                                              [  2%]
  golang/context_test.py ..                                                              [  4%]
  golang/cxx_test.py ..                                                                  [  6%]
  golang/errors_test.py ........                                                         [ 14%]
  golang/fmt_test.py ...                                                                 [ 17%]
  golang/golang_test.py .............................................                    [ 62%]
  golang/io_test.py .                                                                    [ 63%]
  golang/strconv_test.py ..                                                              [ 65%]
  golang/strings_test.py .....                                                           [ 70%]
  golang/sync_test.py .............                                                      [ 83%]
  golang/time_test.py ........                                                           [ 91%]
  golang/pyx/build_test.py FF.                                                           [ 94%]
  golang/pyx/runtime_test.py .                                                           [ 95%]
  gpython/gpython_test.py ssss.                                                          [100%]

  ========================================== FAILURES ==========================================
  _______________________________________ test_pyx_build _______________________________________

      def test_pyx_build():
          pyxuser = testprog + "/golang_pyx_user"
          pyrun(["setup.py", "build_ext", "-i"], cwd=pyxuser)

          # run built test.
          _ = pyout(["-c",
              # XXX `import golang` is a hack: it dynamically loads _golang.so -> libgolang.so,
              # and this way dynamic linker already has libgolang.so DSO found and in
              # memory for all further imports. If we don't, current state of setuptools_dso
              # is that `import pyxuser.test` will fail finding libgolang.so.
              "import golang;" +
  >           "from pyxuser import test; test.main()"], cwd=pyxuser)

  golang/pyx/build_test.py:40:
  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
  golang/golang_test.py:1709: in pyout
      return pyrun(argv, stdin=stdin, stdout=stdout, stderr=stderr, **kw)
  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

  argv = ['-c', 'import golang;from pyxuser import test; test.main()'], stdin = None, stdout = b'', stderr = None
  kw = {'cwd': '/Users/kirr/pygolang/golang/pyx/testprog/golang_pyx_user'}, retcode = 1

      def pyrun(argv, stdin=None, stdout=None, stderr=None, **kw):
          retcode, stdout, stderr = _pyrun(argv, stdin=stdin, stdout=stdout, stderr=stderr, **kw)
          if retcode:
  >           raise RuntimeError(' '.join(argv) + '\n' + (stderr and str(stderr) or '(failed)'))
  E           RuntimeError: -c import golang;from pyxuser import test; test.main()
  E           (failed)

  golang/golang_test.py:1703: RuntimeError
  ------------------------------------ Captured stdout call ------------------------------------
  running build_ext
  cythoning pyxuser/test.pyx to pyxuser/test.cpp
  building 'pyxuser.test' extension
  creating build
  creating build/temp.macosx-10.15-x86_64-3.7
  creating build/temp.macosx-10.15-x86_64-3.7/pyxuser
  clang -Wno-unused-result -Wsign-compare -Wunreachable-code -fno-common -dynamic -DNDEBUG -g -fwrapv -O3 -Wall -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk/usr/include -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk/System/Library/Frameworks/Tk.framework/Versions/8.5/Headers -I/Users/kirr/pygolang -I/Users/kirr/py3.venv/bin/../include/site/python3.7 -I/usr/local/Cellar/python/3.7.6_1/Frameworks/Python.framework/Versions/3.7/include/python3.7m -c pyxuser/test.cpp -o build/temp.macosx-10.15-x86_64-3.7/pyxuser/test.o -std=c++11 -fno-strict-aliasing
  creating build/lib.macosx-10.15-x86_64-3.7
  creating build/lib.macosx-10.15-x86_64-3.7/pyxuser
  clang++ -bundle -undefined dynamic_lookup build/temp.macosx-10.15-x86_64-3.7/pyxuser/test.o -L/Users/kirr/pygolang/golang/runtime -llibgolang -o build/lib.macosx-10.15-x86_64-3.7/pyxuser/test.cpython-37m-darwin.so
  otool -L build/lib.macosx-10.15-x86_64-3.7/pyxuser/test.cpython-37m-darwin.so
  build/lib.macosx-10.15-x86_64-3.7/pyxuser/test.cpython-37m-darwin.so:
  	@loader_path/liblibgolang.0.1.dylib (compatibility version 0.0.0, current version 0.0.0)
  	/usr/lib/libc++.1.dylib (compatibility version 1.0.0, current version 800.7.0)
  	/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1281.0.0)
  install_name_tool -change @loader_path/liblibgolang.0.1.dylib @loader_path/../golang/runtime/liblibgolang.0.1.dylib build/lib.macosx-10.15-x86_64-3.7/pyxuser/test.cpython-37m-darwin.so
  otool -L build/lib.macosx-10.15-x86_64-3.7/pyxuser/test.cpython-37m-darwin.so
  build/lib.macosx-10.15-x86_64-3.7/pyxuser/test.cpython-37m-darwin.so:
  	@loader_path/../golang/runtime/liblibgolang.0.1.dylib (compatibility version 0.0.0, current version 0.0.0)
  	/usr/lib/libc++.1.dylib (compatibility version 1.0.0, current version 800.7.0)
  	/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1281.0.0)
  copying build/lib.macosx-10.15-x86_64-3.7/pyxuser/test.cpython-37m-darwin.so -> pyxuser
  ------------------------------------ Captured stderr call ------------------------------------
  Traceback (most recent call last):
    File "<string>", line 1, in <module>
  ImportError: dlopen(/Users/kirr/pygolang/golang/pyx/testprog/golang_pyx_user/pyxuser/test.cpython-37m-darwin.so, 2): Library not loaded: @loader_path/../golang/runtime/liblibgolang.0.1.dylib
    Referenced from: /Users/kirr/pygolang/golang/pyx/testprog/golang_pyx_user/pyxuser/test.cpython-37m-darwin.so
    Reason: image not found
  _______________________________________ test_dso_build _______________________________________

      def test_dso_build():
          dsouser = testprog + "/golang_dso_user"
          pyrun(["setup.py", "build_dso", "-i"], cwd=dsouser)
          pyrun(["setup.py", "build_ext", "-i"], cwd=dsouser)

          # run built test.
          _ = pyout(["-c",
              # XXX `import golang` is a hack - see test_pyx_build for details.
              "import golang;" +
  >           "from dsouser import test; test.main()"], cwd=dsouser)

  golang/pyx/build_test.py:54:
  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
  golang/golang_test.py:1709: in pyout
      return pyrun(argv, stdin=stdin, stdout=stdout, stderr=stderr, **kw)
  _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

  argv = ['-c', 'import golang;from dsouser import test; test.main()'], stdin = None, stdout = b'', stderr = None
  kw = {'cwd': '/Users/kirr/pygolang/golang/pyx/testprog/golang_dso_user'}, retcode = 1

      def pyrun(argv, stdin=None, stdout=None, stderr=None, **kw):
          retcode, stdout, stderr = _pyrun(argv, stdin=stdin, stdout=stdout, stderr=stderr, **kw)
          if retcode:
  >           raise RuntimeError(' '.join(argv) + '\n' + (stderr and str(stderr) or '(failed)'))
  E           RuntimeError: -c import golang;from dsouser import test; test.main()
  E           (failed)

  golang/golang_test.py:1703: RuntimeError
  ------------------------------------ Captured stdout call ------------------------------------
  running build_dso
  Building DSOs
  building 'dsouser.dso' DSO as build/lib.macosx-10.15-x86_64-3.7/dsouser/libdso.dylib
  creating build
  creating build/temp.macosx-10.15-x86_64-3.7
  creating build/temp.macosx-10.15-x86_64-3.7/dsouser
  clang -Wno-unused-result -Wsign-compare -Wunreachable-code -fno-common -dynamic -DNDEBUG -g -fwrapv -O3 -Wall -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk/usr/include -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk/System/Library/Frameworks/Tk.framework/Versions/8.5/Headers -I/Users/kirr/pygolang -c dsouser/dso.cpp -o build/temp.macosx-10.15-x86_64-3.7/dsouser/dso.o -std=c++11 -fno-strict-aliasing
  creating build/lib.macosx-10.15-x86_64-3.7
  creating build/lib.macosx-10.15-x86_64-3.7/dsouser
  clang++ -dynamiclib -undefined dynamic_lookup build/temp.macosx-10.15-x86_64-3.7/dsouser/dso.o -L/Users/kirr/pygolang/golang/runtime -llibgolang -o build/lib.macosx-10.15-x86_64-3.7/dsouser/libdso.dylib -install_name @loader_path/libdso.dylib
  otool -L build/lib.macosx-10.15-x86_64-3.7/dsouser/libdso.dylib
  build/lib.macosx-10.15-x86_64-3.7/dsouser/libdso.dylib:
  	@loader_path/libdso.dylib (compatibility version 0.0.0, current version 0.0.0)
  	@loader_path/liblibgolang.0.1.dylib (compatibility version 0.0.0, current version 0.0.0)
  	/usr/lib/libc++.1.dylib (compatibility version 1.0.0, current version 800.7.0)
  	/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1281.0.0)
  install_name_tool -change @loader_path/liblibgolang.0.1.dylib @loader_path/../golang/runtime/liblibgolang.0.1.dylib build/lib.macosx-10.15-x86_64-3.7/dsouser/libdso.dylib
  otool -L build/lib.macosx-10.15-x86_64-3.7/dsouser/libdso.dylib
  build/lib.macosx-10.15-x86_64-3.7/dsouser/libdso.dylib:
  	@loader_path/libdso.dylib (compatibility version 0.0.0, current version 0.0.0)
  	@loader_path/../golang/runtime/liblibgolang.0.1.dylib (compatibility version 0.0.0, current version 0.0.0)
  	/usr/lib/libc++.1.dylib (compatibility version 1.0.0, current version 800.7.0)
  	/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1281.0.0)
  copying build/lib.macosx-10.15-x86_64-3.7/dsouser/libdso.dylib -> dsouser
  running build_ext
  cythoning dsouser/test.pyx to dsouser/test.cpp
  building 'dsouser.test' extension
  clang -Wno-unused-result -Wsign-compare -Wunreachable-code -fno-common -dynamic -DNDEBUG -g -fwrapv -O3 -Wall -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk/usr/include -I/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.15.sdk/System/Library/Frameworks/Tk.framework/Versions/8.5/Headers -I/Users/kirr/pygolang -I/Users/kirr/py3.venv/bin/../include/site/python3.7 -I/usr/local/Cellar/python/3.7.6_1/Frameworks/Python.framework/Versions/3.7/include/python3.7m -c dsouser/test.cpp -o build/temp.macosx-10.15-x86_64-3.7/dsouser/test.o -std=c++11 -fno-strict-aliasing
  clang++ -bundle -undefined dynamic_lookup build/temp.macosx-10.15-x86_64-3.7/dsouser/test.o -L/Users/kirr/pygolang/golang/runtime -Lbuild/lib.macosx-10.15-x86_64-3.7/dsouser -llibgolang -ldso -o build/lib.macosx-10.15-x86_64-3.7/dsouser/test.cpython-37m-darwin.so
  otool -L build/lib.macosx-10.15-x86_64-3.7/dsouser/test.cpython-37m-darwin.so
  build/lib.macosx-10.15-x86_64-3.7/dsouser/test.cpython-37m-darwin.so:
  	@loader_path/liblibgolang.0.1.dylib (compatibility version 0.0.0, current version 0.0.0)
  	@loader_path/libdso.dylib (compatibility version 0.0.0, current version 0.0.0)
  	/usr/lib/libc++.1.dylib (compatibility version 1.0.0, current version 800.7.0)
  	/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1281.0.0)
  install_name_tool -change @loader_path/liblibgolang.0.1.dylib @loader_path/../golang/runtime/liblibgolang.0.1.dylib build/lib.macosx-10.15-x86_64-3.7/dsouser/test.cpython-37m-darwin.so
  install_name_tool -change @loader_path/libdso.dylib @loader_path/./libdso.dylib build/lib.macosx-10.15-x86_64-3.7/dsouser/test.cpython-37m-darwin.so
  otool -L build/lib.macosx-10.15-x86_64-3.7/dsouser/test.cpython-37m-darwin.so
  build/lib.macosx-10.15-x86_64-3.7/dsouser/test.cpython-37m-darwin.so:
  	@loader_path/../golang/runtime/liblibgolang.0.1.dylib (compatibility version 0.0.0, current version 0.0.0)
  	@loader_path/./libdso.dylib (compatibility version 0.0.0, current version 0.0.0)
  	/usr/lib/libc++.1.dylib (compatibility version 1.0.0, current version 800.7.0)
  	/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1281.0.0)
  copying build/lib.macosx-10.15-x86_64-3.7/dsouser/test.cpython-37m-darwin.so -> dsouser
  ------------------------------------ Captured stderr call ------------------------------------
  Traceback (most recent call last):
    File "<string>", line 1, in <module>
  ImportError: dlopen(/Users/kirr/pygolang/golang/pyx/testprog/golang_dso_user/dsouser/test.cpython-37m-darwin.so, 2): Library not loaded: @loader_path/../golang/runtime/liblibgolang.0.1.dylib
    Referenced from: /Users/kirr/pygolang/golang/pyx/testprog/golang_dso_user/dsouser/test.cpython-37m-darwin.so
    Reason: image not found
  ========================== 2 failed, 94 passed, 4 skipped in 20.26s ==========================