[clang] Add -fuse-lipo option (PR #121231)

[Ashley Hauck via cfe-commits]

khyperia wrote:

> It is better to add a CLANG_DEFAULT_LIPO cmake option to match the CLANG_DEFAULT_LINKER for -fuse-ld.

Sure, that's a possibility, but in my opinion can be done in a future PR. There's a lot of additional features that can be done in the future:

- CLANG_DEFAULT_LIPO cmake option
- `--lipo-path` commandline argument
- `-fuse-llvm-darwin-tools`, described in the original issue
- better error handling when the lipo tool isn't found
- probably more...

I have a motivation and use case for `-fuse-lipo` and I'd like to get this in first, and we can talk about additional features later - there's no backcompat issues/etc. that require these additional features to be done within this PR.

https://github.com/llvm/llvm-project/pull/121231