glsl: Improve error message for interstage interface block mismatch.

We're now emitting this error from a point where we have easy access
to the name of the block that failed to match, so go ahead and include
that in the error message, as we do for intrastage interface block
mismatches.

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

src/glsl/link_interface_blocks.cpp

@@ -105,7 +105,8 @@ validate_interstage_interface_blocks(struct gl_shader_program *prog,
          continue;
 
       if (var->interface_type != expected_type) {
-         linker_error(prog, "interface block mismatch between shader stages\n");
+         linker_error(prog, "definitions of interface block `%s' do not "
+                      "match\n", var->interface_type->name);
          return;
       }
    }