Enable JIT memory protection on macOS

[knopp]

flutter/flutter#81208

This ensures that memory protection is enabled on both macOS and iOS.

Alternatively we might be able to just keep it enabled on ARM64 target, but i'm not sure it's worth the hassle.

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[chinmaygarde]

I see, this is for a native Apple Silicon build. Makes sense.

[cbracken]

Belated lgtm -- thank you!