[clang] [llvm] [llvm][clang] Propagate VFS through LTO to `PGOOptions` (PR #159671)

[Steven Wu via cfe-commits]

https://github.com/cachemeifyoucan commented:

Is there any way for user to pass in a different VFS to ThinLTO backend? I think this PR just lift the VFS creation one lever higher but I don't see any benefits of doing that?

https://github.com/llvm/llvm-project/pull/159671