Include wchar.h before wrapping memchr

On mingw, wmemcpy() is defined as an inline function using
memcpy(), and the static inline wrapper causes a warning.

```
In file included from include/ruby/ruby.h:39,
                 from win32/file.c:5:
include/ruby/internal/memory.h:284:16: warning: 'ruby_nonempty_memcpy' is static but used in inline function 'wmemcpy' which is not static
  284 | #define memcpy ruby_nonempty_memcpy
      |                ^~~~~~~~~~~~~~~~~~~~
```

win32/file.c

@@ -2,12 +2,12 @@
 /* before stdio.h in ruby/define.h */
 # define MINGW_HAS_SECURE_API 1
 #endif
+#include <wchar.h>
 #include "ruby/ruby.h"
 #include "ruby/encoding.h"
 #include "internal.h"
 #include "internal/error.h"
 #include <winbase.h>
-#include <wchar.h>
 #include <shlwapi.h>
 #include "win32/file.h"