glsl: Fix ast-to-hir for ARB_fragment_coord_conventions

Function ast_declarator_list::hir(), when processing keywords added by
extension ARB_fragment_coord_conventions, made the mistake of checking only if
the extension was __supported by the driver__. The correct behavior is to check
if the extensi0n is __enabled in the parse state__.

NOTE: this is a candidate for the 7.9 branch.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>

src/glsl/ast_to_hir.cpp

@@ -2210,7 +2210,7 @@ ast_declarator_list::hir(exec_list *instructions,
 	    earlier->type = var->type;
 	    delete var;
 	    var = NULL;
-	 } else if (state->extensions->ARB_fragment_coord_conventions
+	 } else if (state->ARB_fragment_coord_conventions_enable
 		    && strcmp(var->name, "gl_FragCoord") == 0
 		    && earlier->type == var->type
 		    && earlier->mode == var->mode) {