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

[Steven Wu via llvm-commits]

cachemeifyoucan 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 https://github.com/llvm/llvm-project/pull/159647

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