[llvm] [DTLTO] [LLVM] Initial DTLTO cache implementation (PR #156433)

[Teresa Johnson via llvm-commits]

teresajohnson wrote:

 > Please also add llvm-lto2 based tests to llvm/test/ThinLTO/X86/dtlto, so that this gets exercised by LLVM tests.

This one was missed - the change needs some llvm-lto2 based tests as well.

https://github.com/llvm/llvm-project/pull/156433