libselinux: Do not use SWIG_CFLAGS when Python bindings are built
    
    Fixes:
    
    Detecting usr/lib64/python3.6/site-packages/selinux/audit2why.cpython-36m-x86_64-linux-gnu.so with not-hardened warnings '
    Hardened: audit2why.cpython-36m-x86_64-linux-gnu.so: FAIL: Gaps were detected in the annobin coverage.  Run with -v to list.
    ' on x86_64