Disable warnings due to deprecated libselinux symbols used by nss and nscd

The SELinux API deprecated several symbols in its 3.1 release, including
security_context_t, matchpathcon, avc_init, and sidput, which are used in
makedb and nscd.  While the usage of these should eventually be replaced by
newer interfaces, this commit disables GCC warnings due to the use of the
above symbols.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>
Tested-by: Carlos O'Donell <carlos@redhat.com>