libselinux: set CFLAGS for pip installation

Explicitly set CFLAGS for the pip install command, similar to calling
setup.py, to ignore known compiler warnings treated as errors, e.g.:

    selinuxswig_python_wrap.c:3593:19: error: 'sidget' is deprecated [-Werror,-Wdeprecated-declarations]
                result = (int)sidget(arg1);
                              ^
    selinuxswig_python_wrap.c:15024:1: error: no previous prototype for function 'PyInit__selinux' [-Werror,-Wmissing-prototypes]
            SWIG_init(void) {
            ^

Signed-off-by: Christian Göttsche <[email protected]>
Acked-by: Petr Lautrbach <[email protected]>

libselinux/src/Makefile

@@ -187,7 +187,7 @@ install: all
  ln -sf --relative $(DESTDIR)$(SHLIBDIR)/$(LIBSO) $(DESTDIR)$(LIBDIR)/$(TARGET)
 
 install-pywrap: pywrap
- $(PYTHON) -m pip install --prefix=$(PREFIX) `test -n "$(DESTDIR)" && echo --root $(DESTDIR) --ignore-installed --no-deps` $(PYTHON_SETUP_ARGS) .
+ CFLAGS="$(CFLAGS) $(SWIG_CFLAGS)" $(PYTHON) -m pip install --prefix=$(PREFIX) `test -n "$(DESTDIR)" && echo --root $(DESTDIR) --ignore-installed --no-deps` $(PYTHON_SETUP_ARGS) .
  install -m 644 $(SWIGPYOUT) $(DESTDIR)$(PYTHONLIBDIR)/selinux/__init__.py
  ln -sf --relative $(DESTDIR)$(PYTHONLIBDIR)/selinux/_selinux$(PYCEXT) $(DESTDIR)$(PYTHONLIBDIR)/_selinux$(PYCEXT)