Fix embarrasing typo in uncaught_exceptions. Update tests to really test this....

Fix embarrasing typo in uncaught_exceptions. Update tests to really test this. Thanks to Peter Klotz for calling my attention to this.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@333467 91177308-0d34-0410-b5e6-96231b3b80d8