Set HXCPP_ARM64 by default when building on Apple Silicon Mac #970

Job	Run time
android	19m 38s
flash-samples	39s
air-samples (4.0.5)	2m 24s
docs	1m 9s
air-samples (4.1.5)	3m 0s
html5-samples	1m 19s
air-samples (4.2.5)	2m 41s
ios	16m 0s
linux	11m 11s
air-samples (4.3.1)	2m 18s
macos	13m 56s
windows	11m 6s
package-haxelib	9m 18s
hashlink-samples (windows-latest)	1m 50s
neko-samples (3.4.7, windows-latest)	6m 44s
hashlink-samples (ubuntu-20.04)	3m 7s
neko-samples (3.4.7, ubuntu-20.04)	1m 26s
hashlink-samples (macos-12)	3m 57s
neko-samples (3.4.7, macos-12)	4m 26s
neko-samples (4.2.5, windows-latest)	6m 47s
neko-samples (4.2.5, ubuntu-20.04)	1m 29s
neko-samples (4.2.5, macos-12)	4m 40s
notify	0s
	2h 9m 5s

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