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

This makes it easy to check if any layout qualifiers are set.

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

src/glsl/ast.h

@@ -457,6 +457,11 @@ struct ast_type_qualifier {
     */
    bool has_interpolation() const;
 
+   /**
+    * Return whether a layout qualifier is present.
+    */
+   bool has_layout() const;
+
    /**
     * \brief Return string representation of interpolation qualifier.
     *