glcpp: Automatically #define GL_core_profile 1 on GLSL 1.50+.

Page 17 of the GLSL 1.50.11 specification states:
"There is a built-in macro definition for each profile the
 implementation supports.  All implementations provide the following
 macro:

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

src/glsl/glcpp/glcpp-parse.y

@@ -2064,6 +2064,9 @@ _glcpp_parser_handle_version_declaration(glcpp_parser_t *parser, intmax_t versio
 		add_builtin_define (parser, "GL_ES", 1);
 	}
 
+	if (version >= 150)
+		add_builtin_define(parser, "GL_core_profile", 1);
+
 	/* Currently, all ES2/ES3 implementations support highp in the
 	 * fragment shader, so we always define this macro in ES2/ES3.
 	 * If we ever get a driver that doesn't support highp, we'll