Adds `-DOSX_NIGHTLY`. With -DOSX_NIGHTLY=ON will produce copies of the zip with generic names: `RawTherapee_macOS_arm64_latest.zip` for the purpose of hyperlinking. This is activated for GitHub Actions automated builds.
* mac: specify catalina on github action
* mac: use clang instead of /path/to/clang
* mac: Exec Architectures --> Architecture Priority
* mac: add an option to generate a universal app
* mac: generate a universal app
* mac: use "Universal" for arch in naming
* mac: remove some braces
* mac: fix gtk3 environment paths
* mac: fix universal url logic
* mac: merge about txts for universal build
* Mac: fix osx version minimums in universal 1
* Mac: update info plist for osx version minima
* Mac: update universal versioning
* Mac: add processor tunings for sandy-ivy bridge
* mac: fix minimum versioning statements
* Mac: fix a paste error
* mac: remove any x/X libs from bundle
* mac: don't get rid of libxcb for cairo
* mac: fix a typo
* mac: revert library removals for cairo
