[clang] [llvm] Skipping host target exports during cross-compilation (PR #209922)

[Martin Storsjö via llvm-commits]

https://github.com/mstorsjo requested changes to this pull request.

Don't merge this, please.

This breaks cases where you cross compile LLVM and then want to cross compile another tool that depends on LLVM - see #205522.

https://github.com/llvm/llvm-project/pull/209922