Basic compile-on-demand support

[pchintalapudi]

By leveraging JITLink, we can obtain lazier compilation provided by LLVM. Because we're using JITLink though, we only support platforms which JITLink can operate on (at the moment only M1 macs and potentially Linux x86-64).

Depends on #46216
Supersedes #44575, #44886, #45038

[Moelf]

https://llvm.org/docs/JITLink.html#jitlink-availability-and-feature-status both seem to have partial?

[vchuravy]

I think COFF and aarch64-linux is coming in LLVM 15

[gbaraldi]

Don't believe those docs so much, they aren't updated that frequently unfortunately