Also works on Apple Silicon. Specific signing values are in a non-committed file, and the ub2 script only notarizes if a "notarize" flag is passed in on the command line.
NOTE: the SDL dylib currently only has x86_64 and arm64, will need extra work to graft those back in and keep the Notary service happy.
SDL 2.0.5 dropped support for macOS 10.5 so target 10.6 instead. The
PPC build uses SDL 2.0.1 so it still targets 10.5. macOS 10.5 (x86,
x86_64) should automatically run the PPC build using Rosetta.
Revert MAN-AT-ARMS' change to SDL 2.0.8 SDL_platform.h that allowed
targeting macOS 10.5 for the sake of PPC. It also incorrectly allowed
x86 and x86_64 to target 10.5 as well. (Also macOS PPC uses separate
headers now.)
