glsl: produce a linker error for a subroutine uniform with no functions.

If a subroutine uniform is declared with no functions backing it,
that isn't legal, so we should fail to link.

Fixes:
GL43-CTS.shader_subroutine.subroutine_uniform_wo_matching_subroutines

Reviewed-by: Chris Forbes <chrisforbes@google.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
1 file changed