[llvm] [CAS] Add llvm-cas tools to inspect on-disk LLVMCAS (PR #166481)

[Amy Kwan via llvm-commits]

amy-kwan wrote:

> There seems to AIX bot failures due to
> 
> ```
> ld: 0711-317 ERROR: Undefined symbol: .flock
> ```
> 
> This is weird since this is supposed to be part of the system_libs. @amy-kwan any idea? This is directly related to #159647

If I remember correctly, the `.flock` issue from last time was resolved after committing https://github.com/llvm/llvm-project/pull/159594, but I wasn't sure why.

I think ultimately, as `flock` is in `libbsd`, committing https://github.com/llvm/llvm-project/pull/159647 makes sense and does indeed fix the build. If it's OK with you, I can reopen this PR.

https://github.com/llvm/llvm-project/pull/166481