[PATCH] Allow _MSC_EXTENSIONS macro on non-Windows targets

[David Majnemer]

  `__wchar_t` is considered a token alias of `wchar_t`.

  https://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/TokenKinds.def?revision=202901&view=markup#l548

http://llvm-reviews.chandlerc.com/D3034