[llvm] [AllocToken] Introduce sanitize_alloc_token attribute and alloc_token metadata (PR #160131)

[Marco Elver via llvm-commits]

melver wrote:

> Would you like to merge it to give bots time to before next patch?

Yeah, once all the other patches (minus builtin) are approved (to make sure no other changes needed), I'd merge them perhaps each with a few hours/1 day distance between them.

https://github.com/llvm/llvm-project/pull/160131