zc.buildout=2.7.1+slapos020 is SlapOS-patched buildout2 with support
for bootstrapping buildout3, required to be able to install buildout3.

Downgrade related eggs to pre-buildout3 versions as well.

Version up zc.buildout, pip and zc.recipe.egg.

Version up slapos.rebootstrap to adapt to buildout3.

See merge request !1587

Revert eb1b1a41 to avoid the use of
`fPIC` flag as it is a "contagious" build option.

To not face the build error "relocation R_X86_64_32 against
.rodata.str1.8 can not be used when making a shared object; recompile
with -fPIC" while building a shared library without fPIC flag, `gcc` is
compiled with `-enable-default-pie` flag (which is a compilation option
used for `gcc` binaries provided by Debian by example, see `gcc -v`).

Since slapos package provides gettext, it is not necessary to build
gettext here. Also slapos package's gettext commands such as msgfmt
may not work with libraries built by a software release, thus remove
LD_LIBRARY_PATH.

Follow https://tech-academy.amarisoft.com/NR_TDD_Pattern.html#Test_4

With newer setuptools that is coming via nexedi/slapos!1550 (44.1.1 -> 67.8.0)
we will need a fix from setuptools-dso 2.10 to handle `python setup develop` well:

Previously with setutools-dso 2.9 and setuptools 67.8.0 built shared libraries were not
copied back into the working tree upon develop install which made anything
using pygolang to fail as e.g.

    $ ../bin/gpython
    Traceback (most recent call last):
      File ".../../bin/gpython", line 20, in <module>
        sys.exit(gpython.main())
      File ".../pygolang/gpython/__init__.py", line 456, in main
        pymain(argv, init)
      File ".../pygolang/gpython/__init__.py", line 223, in pymain
        init()
      File ".../pygolang/gpython/__init__.py", line 447, in init
        import golang
      File ".../pygolang/golang/__init__.py", line 41, in <module>
        from golang._gopath import gimport  # make gimport available from golang
      File ".../pygolang/golang/_gopath.py", line 65, in <module>
        from golang import sync
      File ".../pygolang/golang/sync.py", line 36, in <module>
        from golang._sync import \
    ImportError: liblibgolang.so.0.1: cannot open shared object file: No such file or directory

See https://github.com/mdavidsaver/setuptools_dso/pull/29#issuecomment-1745790761
and https://github.com/mdavidsaver/setuptools_dso/commit/2fdf75f2 for details.

P.S. NOTE that changing version of a setup-egg required egg currently does
_not_ force a rebuild. In other words pushing this change into testnodes won't
make pygolang t o be rebuilt at all. I think this is simply a bug in
slapos.buildout to fix.

/reported-by @xavier_thompson
/cc @jerome, @tomo, @kazuhiko
/reviewed-on nexedi/slapos!1585

See merge request nexedi/slapos!1578

This is done as an alternative to the patch in !1580, as the last
version is already patched.

See merge request nexedi/slapos!1582

without this change, configure would use openssl lib for MD5, sha256sum, ...
if openssl development files are present on the system.

Previously, zstd support was only compiled if zstlib was installed in
the system.

This especially brings support for systems where 'model name' is not
present in /proc/cpuinfo

the previous version was failing like this if lib64 doesn't exist:

libcap: Command 'set -e;cd /opt/slapgrid/shared/libcap/4d09237abd7cb34117fccc1d3c3bc862
[ -d lib64 ] && ln -s lib64 lib' returned non-zero exit status 1