BUILD: Restrict -force_cpusubtype_ALL flag to MacOS X PPC #186

Job	Run time
Xcode (macosx, -scheme ScummVM-macOS -destination 'platform=macOS,arch=x86_64', --disable-nasm --...	36m 46s
Ubuntu (ubuntu-latest, sdl2-config, ccache g++, liba52-dev libcurl4-openssl-dev libfaad-dev libfl...	26m 17s
Xcode (ios7, -scheme ScummVM-iOS CODE_SIGN_IDENTITY="" CODE_SIGNING_ALLOWED=NO, --use-xcframework...	35m 10s
Windows (win32, x86-windows, x86, --enable-discord --enable-faad --enable-gif --enable-mikmod --e...	1h 0m 37s
Ubuntu (ubuntu-20.04, sdl-config, ccache g++-4.8, g++-4.8 liba52-dev libcurl4-openssl-dev libfaad...	24m 20s
Windows (x64, x64, x64-windows, --enable-discord --enable-faad --enable-gif --enable-mikmod --ena...	47m 32s
Windows (arm64, arm64, arm64-windows, --enable-discord --enable-faad --enable-gif --enable-mikmod...	56m 55s
	4h 47m 37s

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