[llvm] [AllocToken] Introduce AllocToken instrumentation pass (PR #156838)

[Hans Wennborg via llvm-commits]

https://github.com/zmodem commented:

Using 64-bit tokens is bad for 32-bit targets (at least with the non-fast ABI). Would 32-bit tokens be enough?

https://github.com/llvm/llvm-project/pull/156838