Tie "location = " to the right stages/versions/extensions. Also add "#define extension 1" extension support and instructions.

git-svn-id: https://cvs.khronos.org/svn/repos/ogl/trunk/ecosystem/public/sdk/tools/glslang@23633 e7fa87d3-cd2b-0410-9028-fcbf551c1848

Test/400.frag

@@ -22,3 +22,13 @@ void main()
     iv4 = textureGatherOffset(isamp2DA, vec3(0.1), ivec2(1), 1+2);
     iv4 = textureGatherOffset(isamp2DA, vec3(0.1), ivec2(i));
 }
+
+layout(location = 4) in vec4 vl; // ERROR, not supported
+
+#ifdef GL_ARB_separate_shader_objects
+#extension GL_ARB_separate_shader_objects : enable
+#endif
+
+layout(location = 4) in vec4 vl2;
+
+layout(location = 3) uniform vec3 uv3;