isspace of Visual Studio C++ assertion failed

HI all,

I noticed that llvm/Support/YAMLTraits.h:501

    isspace(S.front() || isspace(S.back())

expects non-negative chars, but our apps use non-ascii chars so it
failed at runtime.
On linux platform it doesn't.

Would it be fixed in future release? Thanks.


I suggest to add a platform-independent version to StringExtras.h as I
did it for isprint/isPrint in r338034.