glsl: Parse and propagate derivative_group to shader_info

NV_compute_shader_derivatives allow selecting between two possible
arrangements (quads and linear) when calculating derivatives and
certain subgroup operations in case of Vulkan.  So parse and propagate
those up to shader_info.h.

v2: Do not fail when ARB_compute_variable_group_size is being used,
    since we are still clarifying what is the right thing to do here.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

src/compiler/shader_info.h

@@ -252,6 +252,12 @@ typedef struct shader_info {
           *   AddressingModelPhysical64: 64
           */
          unsigned ptr_size;
+
+         /*
+          * Arrangement of invocations used to calculate derivatives in a compute
+          * shader.  From NV_compute_shader_derivatives.
+          */
+         enum gl_derivative_group derivative_group;
       } cs;
 
       /* Applies to both TCS and TES. */