[llvm] [CAS] Add OnDiskGraphDB and OnDiskKeyValueDB (PR #114102)

[Steven Wu via llvm-commits]

cachemeifyoucan wrote:

> Also, could you write some higher level explanation what is the purpose of the code (and the test) that's failing? Maybe this could give them a hint where to look at...

There is an error message `data record span passed the end of the data pool`. If you grep for the message, it is checking if the data record is extended passed the end of the memory mapped region. The test itself is trying to copy structured data from one database file to another, and the failure is either the sizing of the memory mapped region is not correctly tracked, or the data stored is corrupted, or the lookup is from the wrong part of the file. I hope it is not later two logic errors since it is not failing in other systems. 

https://github.com/llvm/llvm-project/pull/114102