[clang] Thread Safety Analysis: Support reentrant capabilities (PR #137133)

[Marco Elver via cfe-commits]

melver wrote:

As additional motivation - quote from a kernel maintainer:

> But I think we should get the infrastructure in once your reentrancy
> support has landed in a release, because with that we can start
> annotation some code and show uses, while also helping to driver more
> requirements.

So there's hope we don't have to also get alias analysis before the Linux kernel use can proceed.

https://github.com/llvm/llvm-project/pull/137133