export missed symbols

Enable `-fvisibility=hidden` and `-fvisibility-inlines-hidden` by default in CI builds to ensure all public symbols are exported correctly.

include/fmt/os.h

@@ -394,7 +394,7 @@ struct ostream_params {
 static constexpr detail::buffer_size buffer_size;
 
 /** A fast output stream which is not thread-safe. */
-class ostream final : private detail::buffer<char> {
+class FMT_API ostream final : private detail::buffer<char> {
  private:
   file file_;
 
@@ -404,7 +404,7 @@ class ostream final : private detail::buffer<char> {
     clear();
   }
 
-  FMT_API void grow(size_t) override final;
+  void grow(size_t) override;
 
   ostream(cstring_view path, const detail::ostream_params& params)
       : file_(path, params.oflag) {