Set HXCPP_ARM64 by default when building on Apple Silicon Mac #965

Job	Run time
android	19m 35s
macos	30m 5s
docs	50s
air-samples (4.0.5)	2m 27s
flash-samples	37s
air-samples (4.1.5)	2m 28s
html5-samples	1m 27s
air-samples (4.2.5)	2m 49s
ios	19m 28s
air-samples (4.3.1)	2m 48s
linux	11m 35s
windows	10m 10s
package-haxelib	3m 5s
hashlink-samples (windows-latest)	1m 53s
hashlink-samples (ubuntu-20.04)	5m 29s
neko-samples (3.4.7, windows-latest)	6m 46s
hashlink-samples (macos-12)	3m 59s
neko-samples (3.4.7, ubuntu-20.04)	5m 9s
neko-samples (3.4.7, macos-12)	6m 47s
neko-samples (4.2.5, windows-latest)	1m 48s
neko-samples (4.2.5, ubuntu-20.04)	58s
neko-samples (4.2.5, macos-12)	7m 20s
notify	0s
	2h 27m 33s

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