[compiler-rt] [llvm] [openmp] [Runtimes] Default build must use its own output dirs (PR #168266)

[Joseph Huber via llvm-commits]

jhuber6 wrote:

> > Yeah, do you think we should move that to LLVM as a tool and pass in a path to the runtime build? Makes it slightly more annoying.
> 
> That is one way, but also consider that libc moved away from this because of this being an ["awkward dependency on the rest of LLVM"](https://discourse.llvm.org/t/rfc-new-headergen-proposal/79679). Now it is written in [Python](https://github.com/llvm/llvm-project/tree/main/libc/utils/hdrgen).

Yeah, that's what I was thinking as well. I'm not sure if we have an ideal solution here, unless we transition to just checking in the generated files and using the tablegen to generate them manually when modified.

https://github.com/llvm/llvm-project/pull/168266