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.)
code/libs/macosx/libSDL2-2.0.0.dylib has 2.0.8 for x86 and x86_64 and
2.0.1 for PPC. Add 2.0.1 headers for PPC with modifed SDL_platform.h to
allow compiling using macOS 10.5 SDK. Using separate headers allows the
engine to check the SDL version for enabling newer SDL features.
