This is not required by the standard (yet), but there seems to be reasonable
support for this being a defect according to CWG discussion, and libstdc++ 7.1
relies on it working.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@304946 91177308-0d34-0410-b5e6-96231b3b80d8