glsl: Add a new ast_type_qualifier::has_auxiliary_storage() method.

"Auxiliary storage qualifiers" is the new term given to "centroid",
"patch", and "sample" by GLSL 4.20/GL_ARB_shading_language_420pack.

Even though we only support "centroid", it's useful to add this now
so that all auxiliary storage qualifiers get handled in the right places
once they're eventually supported.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>

src/glsl/ast.h

@@ -467,6 +467,11 @@ struct ast_type_qualifier {
     */
    bool has_storage() const;
 
+   /**
+    * Return whether an auxiliary storage qualifier is present.
+    */
+   bool has_auxiliary_storage() const;
+
    /**
     * \brief Return string representation of interpolation qualifier.
     *