Add wcscasecmp() and wcsncasecmp() prototypes to wchar.h.

The above prototypes are missing from libc/include/wchar.h but
the functions are present (although with a limited implementation)
in libc.

Change-Id: I1b7c6accfc59ff0f56f3f41a9d3c075e935ac54a
diff --git a/libc/include/wchar.h b/libc/include/wchar.h
index 9b744a5..1361ff5 100644
--- a/libc/include/wchar.h
+++ b/libc/include/wchar.h
@@ -112,6 +112,7 @@
 extern int               vwprintf(const wchar_t *, va_list);
 extern int               vswprintf(wchar_t *, size_t, const wchar_t *, va_list);
 extern size_t            wcrtomb(char *, wchar_t, mbstate_t *);
+extern int               wcscasecmp(const wchar_t *, const wchar_t *);
 extern wchar_t          *wcscat(wchar_t *, const wchar_t *);
 extern wchar_t          *wcschr(const wchar_t *, wchar_t);
 extern int               wcscmp(const wchar_t *, const wchar_t *);
@@ -120,6 +121,7 @@
 extern size_t            wcscspn(const wchar_t *, const wchar_t *);
 extern size_t            wcsftime(wchar_t *, size_t, const wchar_t *, const struct tm *);
 extern size_t            wcslen(const wchar_t *);
+extern int               wcsncasecmp(const wchar_t *, const wchar_t *, size_t);
 extern wchar_t          *wcsncat(wchar_t *, const wchar_t *, size_t);
 extern int               wcsncmp(const wchar_t *, const wchar_t *, size_t);
 extern wchar_t          *wcsncpy(wchar_t *, const wchar_t *, size_t);