add header protection, and two posix compliant prototypes that are provided by R5 libroot.so

git-svn-id: file:///srv/svn/repos/haiku/trunk/current@5814 a95241bf-73f2-0310-859d-f6bbb57e9c96

headers/posix/wchar.h

@@ -4,5 +4,14 @@
  *
  * Distributed under the terms of the MIT license
  */
+#ifndef _WCHAR_H
+#define _WCHAR_H
 
 #include <wchar_t.h>
+
+#include <size_t.h>
+
+int		mbsinit(const mbstate_t *);
+size_t	wcrtomb(char *, wchar_t, mbstate_t *);
+
+#endif /* _WCHAR_H */