Avoid a call to PyTuple_GET_ITEM() to get the item array pointer if CYTHON_ASSUME_SAFE_MACROS is disabled.
See https://github.com/cython/cython/issues/3701

Rebased 1bb26b96 for cython 0.29.x,
and made conditional to Python 3.  This does not solve the original staticmethod problem
in Python 2 but it does resolve classmethod problems in Python 3.9.  Therefore, it unbreaks
other packages on Python 3.9, improves overall state for Python 3 and does not introduce
regressions in Python 2.

This reverts commit 66773260.

classmethod() should fall back to calling PyClassMethod_New() instead of deciding for itself that the type is invalid. (GH-3660)

classmethod() should fall back to calling PyClassMethod_New() instead of deciding for itself that the type is invalid. (GH-3660)

Use a more efficient way to check for PyCFunction and CyFunction at the same time since checking for PyCFunction became more costly in Py3.9.

The names of Cython's internal types (functions, generator, coroutine, etc.) are now prefixed with the shared module name, instead of making them look like homeless builtins.
See https://bugs.python.org/issue20204
See https://github.com/python/cpython/commit/490055a1673b524da2ebe2312f072aba2a826036

Add "tp_pypy_flags" field to PyTypeObject struct when compiling in PyPy 6.0+ in order to avoid C compiler warnings about an uninitialised struct field.

Prevent calling PyObject_GC_Track() in __Pyx_CyFunction_New() when instantiating a fused function before the object fields of the fused function subtype are fully initialised.
See https://bugs.python.org/issue38392
Closes GH-3215.
Supersedes GH-3216.

Sprinkle lots of branch prediction hints in places where exceptions are being handled or otherwise exceptional cases occur.

Prevent calling PyObject_GC_Track() in __Pyx_CyFunction_New() when instantiating a fused function before the object fields of the fused function subtype are fully initialised.
See https://bugs.python.org/issue38392
Closes GH-3215.
Supersedes GH-3216.

Relaxed some of the checks of fused functions to be consistent with general CyFunctions.

```
 # cython: binding=True
def f(arg):
  pass

class C:  # or cdef class...
  f = f
  def g(self, ...):
    pass

C.f(something) or C().f() # doesn't enforce any checks on the type of arg -
 # with a fused function it does.

C.g(something) # assumes that self is "C" (at least for a cdef class)
 # but doesn't check it. A fused function enforces that it is C.

C.f() # fails with a fused function claiming too few arguments, even though
 # default arguments may make it a valid call
```

Obviously removing checks does make things a little less safe, but it
is consistent with the more general function behaviour. (I'm doing
this as part of a broad plan to abuse fused functions to be a bit
cleverer about decorators, but I don't think the motivation hugely
matters for this change)

* Fixed issue where fused functions didn't register as cyfunctions

Issue https://github.com/cython/cython/issues/3384

This happened where Cython was using a shared API because the
CyFunction type imported from the shared api wasn't the same as
used to initialize the fused function tp_base.

* Fixed issue where fused functions didn't register as cyfunctions

Issue https://github.com/cython/cython/issues/3384

This happened where Cython was using a shared API because the
CyFunction type imported from the shared api wasn't the same as
used to initialize the fused function tp_base.

Default arguments are now copied when the bound fused function is created.

Default arguments are now copied when the bound fused function is created.

Use correct "Py_mp_subscript" type slot for getitem() method instead of "Py_mp_ass_subscript" (which is for assignments).

Fix "unused" C compiler warning for "__pyx_FusedFunction_mapping_methods" when using the limited C-API.

* Add more limited api support
* Fix Fused Functions
* Fixed profile
* Use PyModule_GetDict
* Simplify __Pyx_Globals
* Address issues in CommonStructures
* ifdef guard CyFunction and FusedFunction

This should complete #3171 in silencing -Wmissing-field-initializers.

This should complete #3171 in silencing -Wmissing-field-initializers.

Minor cleanup regarding __Pyx_PyMethod_New