[flang-commits] [flang] [flang] Fix finding system install of LLVM/Clang/MLIR in standalone builds (PR #120914)

[Slava Zakharin via flang-commits]

vzakhari wrote:

> Ah, sorry. Reverted now.

This change should be related: https://github.com/llvm/llvm-zorg/pull/170
The relative paths have to be weird (i.e. relative to the src dir), so that `find_package` can work with them.

Sorry, it was long time ago, so I forgot about it.

https://github.com/llvm/llvm-project/pull/120914