[llvm] [IR] Introduce `llvm.strlen.*` intrinsics (PR #135792)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

This needs an RFC, I expect opposition to the introduction of intrinsics for string libcalls (that are not builtins required even in freestanding environments).

https://github.com/llvm/llvm-project/pull/135792