glcpp: Add built-in define for ARB_shader_image_load_store.

Reviewed-by: Paul Berry <stereotype441@gmail.com>

src/glsl/glcpp/glcpp-parse.y

@@ -2126,6 +2126,9 @@ _glcpp_parser_handle_version_declaration(glcpp_parser_t *parser, intmax_t versio
 
               if (extensions->ARB_compute_shader)
                  add_builtin_define(parser, "GL_ARB_compute_shader", 1);
+
+	      if (extensions->ARB_shader_image_load_store)
+	         add_builtin_define(parser, "GL_ARB_shader_image_load_store", 1);
 	   }
 	}