The previous fix introduced a not-yet-understood regression in compiling
CodePeer. For now, we attempt a quick workaround for the problem.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

	* sem_util.adb (Build_Discriminant_Reference): In the unexpected
	case where we previously would fail an assertion, we instead
	revert to the old behavior.