Reconfiguring with a different --with-gtkabi or --with-sdlabi doesn't
trigger a remake. Generate an (unused) CONFIG_GTKABI/CONFIG_SDLABI
so config-host.h will actually give 'make' something to trigger on.

Signed-off-by: Cole Robinson <crobinso@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>