re PR c++/59281 (attribute((constructor)) accepts enum class as integer constant)

	PR c++/59281
	* g++.dg/ext/attr-constructor1.C: New.

From-SVN: r232704

gcc/testsuite/g++.dg/ext/attr-constructor1.C

+// PR c++/59281
+// { dg-do compile { target c++11 } }
+
+enum class E : int { prio = 666 };
+void f (int) __attribute__((constructor(E::prio))); // { dg-error "integer" }