macros.python*: make LDFLAGS propagated whenever CFLAGS are
    
    This is to ensure the right linker flags get propagated into binaries
    accompanying python packages whenever distutils (or similar, env.
    variables provided build flags aware) module is delegated to build them
    (e.g. https://bugzilla.redhat.com/show_bug.cgi?id=1541106).  Instead of
    using "%{__global_ldflags}" as the seed for the respective env. variable
    one-off application, which would be a direct parallel to "%{optflags}"
    seeding CFLAGS, use rather "${RPM_LD_FLAGS}" and "${RPM_OPT_FLAGS}",
    as these are not directly bound to macros out of rpm proper (like
    it would have been, e.g., on redhat-rpm-config package otherwise).
    
    Signed-off-by: Jan Pokorný <jpokorny@redhat.com>