glsl/cs: Initialize gl_LocalInvocationIndex in main()
glsl/cs: Initialize gl_LocalInvocationIndex in main()

We initialize gl_LocalInvocationIndex based on the extension spec
formula:

    gl_LocalInvocationIndex =
        gl_LocalInvocationID.z * gl_WorkGroupSize.x * gl_WorkGroupSize.y +
        gl_LocalInvocationID.y * gl_WorkGroupSize.x +
        gl_LocalInvocationID.x;

https://www.opengl.org/registry/specs/ARB/compute_shader.txt

Signed-off-by: Jordan Justen <a79006884ba9cf5f4f7fcbb92a15b208780d8c97@intel.com>
Reviewed-by: Tapani Pälli <cdcb67a5e49297de94340ca09f25994bd5e7f762@intel.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler