[libc++] Suggested fix for #167977

Handle the same guards used by musl libc to conditionally compile the 'Strtonum functions'

Author: reactive-firewall

libcxx/include/__locale_dir/support/linux.h

@@ -83,15 +83,30 @@ inline _LIBCPP_HIDE_FROM_ABI __lconv_t* __localeconv(__locale_t& __loc) {
 // Strtonum functions
 //
 inline _LIBCPP_HIDE_FROM_ABI float __strtof(const char* __nptr, char** __endptr, __locale_t __loc) {
+#if !_LIBCPP_HAS_MUSL_LIBC || defined(_GNU_SOURCE)
   return ::strtof_l(__nptr, __endptr, __loc);
+#else
+  (void)__loc;
+  return ::strtof(__nptr, __endptr);
+#endif
 }
 
 inline _LIBCPP_HIDE_FROM_ABI double __strtod(const char* __nptr, char** __endptr, __locale_t __loc) {
+#if !_LIBCPP_HAS_MUSL_LIBC || defined(_GNU_SOURCE)
   return ::strtod_l(__nptr, __endptr, __loc);
+#else
+  (void)__loc;
+  return ::strtod(__nptr, __endptr);
+#endif
 }
 
 inline _LIBCPP_HIDE_FROM_ABI long double __strtold(const char* __nptr, char** __endptr, __locale_t __loc) {
+#if !_LIBCPP_HAS_MUSL_LIBC || defined(_GNU_SOURCE)
   return ::strtold_l(__nptr, __endptr, __loc);
+#else
+  (void)__loc;
+  return ::strtold(__nptr, __endptr);
+#endif
 }
 
 inline _LIBCPP_HIDE_FROM_ABI long long __strtoll(const char* __nptr, char** __endptr, int __base, __locale_t __loc) {