Make get_path_string more portable

include/fmt/std.h

@@ -64,8 +64,12 @@ FMT_BEGIN_NAMESPACE
 
 namespace detail {
 
-template <typename Char> auto get_path_string(const std::filesystem::path& p) {
-  return p.string<Char>();
+template <typename Char, typename PathChar> auto get_path_string(
+  const std::filesystem::path& p, const std::basic_string<PathChar>& native) {
+  if constexpr (std::is_same_v<Char, char> && std::is_same_v<PathChar, wchar_t>)
+    return to_utf8<wchar_t>(native, to_utf8_error_policy::replace);
+  else
+    return p.string<Char>();
 }
 
 template <typename Char>
@@ -75,10 +79,6 @@ void write_escaped_path(basic_memory_buffer<Char>& quoted,
 }
 
 #  ifdef _WIN32
-template <> inline auto get_path_string<char>(const std::filesystem::path& p) {
-  return to_utf8<wchar_t>(p.native(), to_utf8_error_policy::replace);
-}
-
 template <>
 inline void write_escaped_path<char>(memory_buffer& quoted,
                                      const std::filesystem::path& p) {
@@ -130,7 +130,7 @@ template <typename Char> struct formatter<std::filesystem::path, Char> {
     detail::handle_dynamic_spec<detail::width_checker>(specs.width, width_ref_,
                                                        ctx);
     if (!debug_) {
-      auto s = detail::get_path_string<Char>(p);
+      auto s = detail::get_path_string<Char>(p, p.native());
       return detail::write(ctx.out(), basic_string_view<Char>(s), specs);
     }
     auto quoted = basic_memory_buffer<Char>();