[PATCH] [libcxx] Fix ctype_byname<wchar_t>::do_is() mask checking.

[Jon Roelofs]

Here's v2 of this patch: http://reviews.llvm.org/D5081

(This is a rebased version of: https://gist.github.com/jroelofs/8c6091f79ae2327f1ccb)

http://reviews.llvm.org/D5071