[libc++] Fix the locale base API on Linux with musl (#128936)

Since `363bfd6090b0 ([libc++] Use the new locale base API on Linux
(#128007), 2025-02-24)`, musl targets will fail to build with errors
due to missing strtoll_l functions.

Co-authored-by: Pirama Arumuga Nainar <[email protected]>

Author: androm3da

libcxx/include/__locale_dir/support/linux.h

@@ -95,12 +95,22 @@ inline _LIBCPP_HIDE_FROM_ABI long double __strtold(const char* __nptr, char** __
 }
 
 inline _LIBCPP_HIDE_FROM_ABI long long __strtoll(const char* __nptr, char** __endptr, int __base, __locale_t __loc) {
+#if !_LIBCPP_HAS_MUSL_LIBC
   return ::strtoll_l(__nptr, __endptr, __base, __loc);
+#else
+  (void)__loc;
+  return ::strtoll(__nptr, __endptr, __base);
+#endif
 }
 
 inline _LIBCPP_HIDE_FROM_ABI unsigned long long
 __strtoull(const char* __nptr, char** __endptr, int __base, __locale_t __loc) {
+#if !_LIBCPP_HAS_MUSL_LIBC
   return ::strtoull_l(__nptr, __endptr, __base, __loc);
+#else
+  (void)__loc;
+  return ::strtoull(__nptr, __endptr, __base);
+#endif
 }
 
 //