[libc] Fix internal::wcschr() return type.

The exported function is using a similar white lie for convenience, so the internal function may as well rather than adding const casts.

Author: enh-google

libc/src/wchar/wchar_utils.h

@@ -17,7 +17,7 @@
 namespace LIBC_NAMESPACE_DECL {
 namespace internal {
 
-LIBC_INLINE static wchar_t *wcschr(const wchar_t *s, wchar_t c) {
+LIBC_INLINE static const wchar_t *wcschr(const wchar_t *s, wchar_t c) {
   for (; *s && *s != c; ++s)
     ;
   return (*s == c) ? s : nullptr;
@@ -29,7 +29,7 @@ LIBC_INLINE static size_t wcsspn(const wchar_t *s1, const wchar_t *s2,
                                  bool not_match_set) {
   size_t i = 0;
   for (; s1[i]; ++i) {
-    bool in_set = wcschr(s1[i], s2);
+    bool in_set = internal::wcschr(s2, s1[i]);
     if (in_set == not_match_set)
       return i;
   }