[llvm] [CAS] Add OnDiskTrieRawHashMap (PR #114100)

[Paul Kirth via llvm-commits]

https://github.com/ilovepi approved this pull request.

LGTM. I just have the 1 Q on the format that I left in line, w.r.t the header layout. 

https://github.com/llvm/llvm-project/pull/114100