libselinux: Use Python distutils to install SELinux python bindings

Follow officially documented way how to build C extension modules using
distutils - https://docs.python.org/3.8/extending/building.html#building

Fixes:

- selinux python module fails to load when it's built using SWIG-4.0:

>>> import selinux
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib64/python3.7/site-packages/selinux/__init__.py", line 13, in <module>
    from . import _selinux
ImportError: cannot import name '_selinux' from 'selinux' (/usr/lib64/python3.7/site-packages/selinux/__init__.py)

SWIG-4.0 changed (again?) its behavior so that it uses: from . import _selinux
which looks for _selinux module in the same directory as where __init__.py is -
$(PYLIBDIR)/site-packages/selinux. But _selinux module is installed into
$(PYLIBDIR)/site-packages/ since a9604c30a5e2f ("libselinux: Change the location
of _selinux.so").

- audit2why python module fails to build with Python 3.8

cc -O2 -g -pipe -Wall -Werror=format-security -Wp,-D_FORTIFY_SOURCE=2 -Wp,-D_GLIBCXX_ASSERTIONS -fexceptions -fstack-protector-strong -grecord-gcc-switches -specs=/usr/lib/rpm/redhat/redhat-hardened-cc1 -specs=/usr/lib/rpm/redhat/redhat-annobin-cc1 -m64 -mtune=generic -fasynchronous-unwind-tables -fstack-clash-protection -fcf-protection -DOVERRIDE_GETTID=0 -I../include -D_GNU_SOURCE -DDISABLE_RPM -DNO_ANDROID_BACKEND -DUSE_PCRE2 -DPCRE2_CODE_UNIT_WIDTH=8  -Wl,-z,relro -Wl,--as-needed  -Wl,-z,now -specs=/usr/lib/rpm/redhat/redhat-hardened-ld -L. -shared -o python-3.8audit2why.so python-3.8audit2why.lo -lselinux -l:libsepol.a  -Wl,-soname,audit2why.so,--version-script=audit2why.map,-z,defs
/usr/bin/ld: python-3.8audit2why.lo: in function `finish':
/builddir/build/BUILD/libselinux-2.9/src/audit2why.c:166: undefined reference to `PyArg_ParseTuple'
/usr/bin/ld: python-3.8audit2why.lo: in function `_Py_INCREF':
/usr/include/python3.8/object.h:449: undefined reference to `_Py_NoneStruct'
/usr/bin/ld: /usr/include/python3.8/object.h:449: undefined reference to `_Py_NoneStruct'
/usr/bin/ld: python-3.8audit2why.lo: in function `check_booleans':
/builddir/build/BUILD/libselinux-2.9/src/audit2why.c:84: undefined reference to `PyExc_RuntimeError'
...

It's related to the following Python change
https://docs.python.org/dev/whatsnew/3.8.html#debug-build-uses-the-same-abi-as-release-build

Python distutils adds correct link options automatically.

- selinux python module doesn't provide any Python metadata

When selinux python module was built manually, it didn't provide any metadata.
distutils takes care about that so that selinux Python module is visible for
pip:

$ pip3 list | grep selinux
selinux              2.9

Signed-off-by: Petr Lautrbach <plautrba@redhat.com>
3 files changed