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.450.subgroupClusteredNeg.comp

@@ -0,0 +1,39 @@
+#version 450
+
+#extension GL_KHR_shader_subgroup_clustered: enable
+
+layout (local_size_x = 8) in;
+
+layout(binding = 0) buffer Buffers
+{
+    vec4  f4;
+    ivec4 i4;
+    uvec4 u4;
+    dvec4 d4;
+} data[4];
+
+void main()
+{
+    int a = 1;
+    const int aConst = 1;
+
+    uint invocation = (gl_SubgroupInvocationID + gl_SubgroupSize) % 4;
+
+    data[invocation].f4.xy  = subgroupClusteredAdd(data[1].f4.xy, 0);          // ERROR, less than 1
+
+    data[invocation].f4.x   = subgroupClusteredMul(data[0].f4.x, 3);           // ERROR, not a power of 2
+
+    data[invocation].i4.xy  = subgroupClusteredMin(data[1].i4.xy, 8);
+    data[invocation].i4.xyz = subgroupClusteredMin(data[2].i4.xyz, 6);         // ERROR, not a power of 2
+
+    data[invocation].f4.x   = subgroupClusteredMax(data[0].f4.x, -1);          // ERROR, less than 1
+
+    data[invocation].i4     = subgroupClusteredAnd(data[3].i4, -3);            // ERROR, less than 1
+
+    data[invocation].i4.x   = subgroupClusteredOr(data[0].i4.x, a);            // ERROR, not constant
+    data[invocation].i4.xy  = subgroupClusteredOr(data[1].i4.xy, aConst);
+
+    data[invocation].i4.x   = subgroupClusteredXor(data[0].i4.x, 1 + a);       // ERROR, not constant
+    data[invocation].i4.xy  = subgroupClusteredXor(data[1].i4.xy, aConst + a); // ERROR, not constant
+    data[invocation].i4.xyz = subgroupClusteredXor(data[2].i4.xyz, 1 + aConst);
+}