Apparently XFAIL tests that are supposed to fail to compile can be problematic. They still get compiled, and if the compile succeeds, the buildbots complain. Replace the XFAIL with #error.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@267591 91177308-0d34-0410-b5e6-96231b3b80d8
7 files changed