[clang] [clang-tools-extra] In compilation databases, add support for relative directories (PR #69856)

[Fangrui Song via cfe-commits]

MaskRay wrote:

We need an update to the documentation `JSONCompilationDatabase` and formal description of the problem you have seen.

Your Buck2 feature is not blocked. You can use `/proc/self/cwd`, which is probably unavoidable if you use other features that require reproducible builds (https://maskray.me/blog/2022-08-14-dwarf-in-reproducible-builds has some description).

https://github.com/llvm/llvm-project/pull/69856