SPV: Further refine OpenGL vs. Vulkan differences for SPIR-V.

Includes adding test cases to verify the differences.

Test/glspv.vert

@@ -0,0 +1,20 @@
+#version 450
+
+layout(push_constant) uniform Material { int a; } mat;            // ERROR, can't use push_constant
+
+layout(set = 0, binding = 0, std140) uniform Bt1 { int a; } bt1;
+layout(set = 1, binding = 0, std140) uniform Bt2 { int a; } bt2;  // ERROR, set has to be 0
+
+layout(shared) uniform Bt3 { int a; } bt3;                        // ERROR, no shared
+layout(packed) uniform Bt4 { int a; } bt4;                        // ERROR, no shared
+
+void main()
+{
+    gl_VertexIndex;   // ERROR, not preset
+    gl_InstanceIndex; // ERROR, not present
+    gl_VertexID;
+    gl_InstanceID;
+    gl_DepthRangeParameters; // ERROR, not present
+}
+
+uniform sampler s; // ERROR, no sampler