glsl: Add error message for intrastage interface block mismatch.

Previously we failed to link (which is correct), but we did not output
an error message, which could have been confusing for users.

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

src/glsl/linker.h

@@ -61,7 +61,8 @@ link_uniform_blocks(void *mem_ctx,
                     struct gl_uniform_block **blocks_ret);
 
 bool
-validate_intrastage_interface_blocks(const gl_shader **shader_list,
+validate_intrastage_interface_blocks(struct gl_shader_program *prog,
+                                     const gl_shader **shader_list,
                                      unsigned num_shaders);
 
 bool