Add test case for PR16785.

Thanks for Dimitry Andric, Rafael Espindola, and Benjamin Kramer
for providing and progressively reducing the test case!



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191782 91177308-0d34-0410-b5e6-96231b3b80d8
Reverts commit r190808 and r190556.

The use of these features in clang has been reverted.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191785 91177308-0d34-0410-b5e6-96231b3b80d8