Apple Silicon would benefit from JIT

[cognominal]

Apple sets aside an additional reserved register in addition to the ones asked by the ARM docs. lizmat proposes a configuration flag to both address JITing ARM64 and Apple Silicon at once.

See #1395

From the Apple documentation

https://developer.apple.com/documentation/apple_silicon/porting_just-in-time_compilers_to_apple_silicon https://developer.apple.com/documentation/xcode/writing_arm64_code_for_apple_platforms

The ARM standard delegates certain decisions to platform designers. Apple platforms adhere to the following choices:

The platforms reserve register x18. Don’t use this register.

frame pointer register (x29) must always address a valid frame record.