spirv: handle gl_SampleMask
spirv: handle gl_SampleMask

SPIR-V maps both gl_SampleMask and gl_SampleMaskIn to the same
builtin (SampleMask). The only way to tell which one we are dealing with
is to check if it is an input or an output.

Fixes:
dEQP-VK.pipeline.multisample_shader_builtin.sample_mask.write.*

Reviewed-by: Jason Ekstrand <68c46a606457643eab92053c1c05574abb26f861@jlekstrand.net>
Reviewed-by: Anuj Phogat <e2026475996c48f0b97fd37e84129b3912980428@gmail.com>
Reviewed-by: Lionel Landwerlin <9463032a5b99ffad10f36631678a833369a311b5@intel.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler