gl_WorkGroupSize must be a constant

[kevinboulain]

(Thanks for glsl.meta.slang it's quite helpful to port over GLSL code.)

This shader:

import "glsl";

[shader("compute")] [numthreads(256, 1, 1)] void compute() {
  const uint x = gl_WorkGroupSize.x;
}

When compiled like this (v2024.1.6) and passed through spirv-val will complain that gl_WorkGroupSize isn't decorated as it should:

slangc compute.slang -target spirv -o compute.spv -emit-spirv-directly -fvk-use-entrypoint-name
spirv-val compute.spv 
error: line 7: BuiltIn decoration on target <id> '9[%gl_WorkGroupSize]' must be a constant for WorkgroupSize
  OpDecorate %gl_WorkGroupSize BuiltIn WorkgroupSize