Add some tests to ensure that the __regex_word does not conflict with any of ctype_base's values.
Hopefully this will catch cases like https://llvm.org/bugs/show_bug.cgi?id=26476 in the future.



git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@260527 91177308-0d34-0410-b5e6-96231b3b80d8