Add specialization constant work group size test for MSL.

reference/shaders-msl/comp/specialization-constant-workgroup.comp

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+#include <metal_stdlib>
+#include <simd/simd.h>
+
+using namespace metal;
+
+constant uint _13_tmp [[function_constant(3)]];
+constant uint _13 = is_function_constant_defined(_13_tmp) ? _13_tmp : 1u;
+constant uint _15_tmp [[function_constant(20)]];
+constant uint _15 = is_function_constant_defined(_15_tmp) ? _15_tmp : 1u;
+constant uint3 gl_WorkGroupSize = uint3(_13, 10u, _15);
+
+struct SSBO
+{
+    uint3 wg_size;
+};
+
+kernel void main0(device SSBO& _10 [[buffer(0)]])
+{
+    _10.wg_size = gl_WorkGroupSize;
+}
+

shaders-msl/comp/specialization-constant-workgroup.comp

@@ -0,0 +1,12 @@
+#version 310 es
+layout(local_size_x_id = 3, local_size_y = 10, local_size_z_id = 20) in;
+
+layout(binding = 0) buffer SSBO
+{
+	uvec3 wg_size;
+};
+
+void main()
+{
+	wg_size = gl_WorkGroupSize;
+}