Support compiling universal macOS binaries.

[jchv]

While Rosetta 2 works fine for most intents and purposes, it seems that gamepads do not work properly under Rosetta 2 applications. (#148)

Relevant information: Building a universal macOS binary.

(Feel free to assign me. I plan on taking this on later tonight.)

[Screwtapello]

See also https://github.com/higan-emu/higan/issues/149