G M:  Restore the ability for libcxx to compile again on mingw 64.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@190837 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/cwchar b/include/cwchar
index 90eae75..9f51587 100644
--- a/include/cwchar
+++ b/include/cwchar
@@ -106,7 +106,7 @@
 #include <__config>
 #include <cwctype>
 #include <wchar.h>
-#ifdef _LIBCPP_MSVCRT
+#if defined(_LIBCPP_MSVCRT) || defined(__MINGW32__)
 #include <support/win32/support.h> // pull in *swprintf defines
 #endif // _LIBCPP_MSVCRT