fix clang-cl warnings in fileutils.c

Author: chris-eibl

Python/fileutils.c

@@ -55,8 +55,9 @@ int _Py_open_cloexec_works = -1;
 
 // mbstowcs() and mbrtowc() errors
 static const size_t DECODE_ERROR = ((size_t)-1);
+#ifdef HAVE_MBRTOWC
 static const size_t INCOMPLETE_CHARACTER = (size_t)-2;
-
+#endif
 
 static int
 get_surrogateescape(_Py_error_handler errors, int *surrogateescape)
@@ -129,7 +130,7 @@ is_valid_wide_char(wchar_t ch)
         // Reject lone surrogate characters
         return 0;
     }
-    if (ch > MAX_UNICODE) {
+    if (sizeof(ch) > 2 && ch > MAX_UNICODE) {
         // bpo-35883: Reject characters outside [U+0000; U+10ffff] range.
         // The glibc mbstowcs() UTF-8 decoder does not respect the RFC 3629,
         // it creates characters outside the [U+0000; U+10ffff] range: