crt: mbctype.h: add missing _MB_CP_UTF8

This constant is used with _setmbcp to set multibyte code page
to UTF-8. Note, however, that multibyte functions declared in
mbctype.h and mbstring.h cannot operate on UTF-8 strings.

Signed-off-by: Kirill Makurin <[email protected]>
Signed-off-by: LIU Hao <[email protected]>

Author: maiddaisuki

mingw-w64-headers/crt/mbctype.h

@@ -48,6 +48,9 @@ extern "C" {
 #define _MB_CP_OEM -2
 #define _MB_CP_ANSI -3
 #define _MB_CP_LOCALE -4
+#ifdef _UCRT
+#define _MB_CP_UTF8 65001
+#endif
 
 #ifndef _MBCTYPE_DEFINED
 #define _MBCTYPE_DEFINED