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

include/support/win32/support.h

@@ -15,11 +15,16 @@
    Functions and constants used in libc++ that are missing from the Windows C library.
   */
 
-#include <cwchar>  // mbstate_t
+#include <wchar.h>  // mbstate_t
 #include <cstdarg> // va_ macros
 #define swprintf _snwprintf
 #define vswprintf _vsnwprintf
 
+#ifndef NOMINMAX
+#define NOMINMAX
+#endif
+#include <Windows.h>
+
 extern "C" {
 
 int vasprintf( char **sptr, const char *__restrict fmt, va_list ap );