Enable GL_KHR_shader_subgroup properly

(and GL_NV_shader_subgroup_partitioned) based on GL/ES version
instead of predicating it on vulkan SPV generation

Also add AST testing.
The glsl.450.subgroup* files are largely the same as the spv.subgroup*
The glsl.es320.subgroup* files are the same as the 450 versions, but modified to be ES compatible.

Test/glsl.es320.subgroupClusteredNeg.comp

@@ -0,0 +1,34 @@
+#version 320 es
+
+#extension GL_KHR_shader_subgroup_clustered: enable
+
+layout (local_size_x = 8) in;
+
+layout(binding = 0) buffer Buffers
+{
+    vec4  f4;
+    ivec4 i4;
+    uvec4 u4;
+} data[4];
+
+void main()
+{
+    int a = 1;
+    const int aConst = 1;
+
+    uint invocation = (gl_SubgroupInvocationID + gl_SubgroupSize) % 4u;
+
+    data[0].f4.xy  = subgroupClusteredAdd(data[1].f4.xy, 0u);          // ERROR, less than 1
+
+    data[0].f4.x   = subgroupClusteredMul(data[0].f4.x, 3u);           // ERROR, not a power of 2
+
+    data[1].i4.xy  = subgroupClusteredMin(data[1].i4.xy, 8u);
+    data[1].i4.xyz = subgroupClusteredMin(data[2].i4.xyz, 6u);         // ERROR, not a power of 2
+
+    data[3].i4.x   = subgroupClusteredOr(data[0].i4.x, uint(a));            // ERROR, not constant
+    data[3].i4.xy  = subgroupClusteredOr(data[1].i4.xy, uint(aConst));
+
+    data[0].i4.x   = subgroupClusteredXor(data[0].i4.x, uint(1 + a));       // ERROR, not constant
+    data[0].i4.xy  = subgroupClusteredXor(data[1].i4.xy, uint(aConst + a)); // ERROR, not constant
+    data[0].i4.xyz = subgroupClusteredXor(data[2].i4.xyz, uint(1 + aConst));
+}