st/nine: Implement fallback behaviour when rts and ds don't match
st/nine: Implement fallback behaviour when rts and ds don't match

This seems to be the behaviour on Win. Previous behaviour led
to different issues depending on the driver.

Reviewed-by: Tiziano Bacocco <2a82869f7317db18254323fa12ab4a27cc39e639@gmail.com>
Signed-off-by: Axel Davy <2b6ef604b998fb81662f85c329e4fc020eae8e5d@ens.fr>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler