Add RPM macros for compiler/linker flags
    
    Backport is quite useful so specs don't need to diverge between
    branches.
    
    Chery-Pick note: No documentation backport since there was no
    documentation back then in F27 so backporting means writing new one.
    
    (cherry picked from commit fa08f0e5a18d27663084a35e992083e8e38cc2a4)
    Reported-by: Jens Petersen <petersen@redhat.com>
    Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1546643
    Signed-off-by: Igor Gnatenko <ignatenkobrain@fedoraproject.org>