Pyxel can't be compiled on Intel Mac
On Intel Mac with the recent Xcode environment, Pyxel can't be compiled. The situation is similar for Github Actions' hosted runner.
The error happens while compiling SDL2 via rust-sdl2 and the error message is ``ld: library not found for -lstdc++``.

In the case of declaring ``CXXFLAGS="-stdlib=libc++"``, compilation itself is finished without errors, but runtime error ``symbol not found in flat namespace'___isPlatformVersionAtLeast'`` happens when the Python module wrapped by PyO3 and Maturin is imported.

Regardless of declaring the env variable, Pyxel can be compiled and works on Apple Silicon Mac.

Does anyone know how to resolve this issue?
(Especially @messense , do you have any idea?)
