[clang] [compiler-rt] [llvm] [CMake] Use Clang to infer the target triple (PR #89425)

[YunQiang Su via cfe-commits]

wzssyqa wrote:

> @wzssyqa Is it OK with you if I go ahead and merge this PR? I plan to follow up with further improvements but this is necessary to fix the build of LLVM runtime libraries in the bootstrapping build.

It is OK for me, while I have no permission to approve such a patch.

https://github.com/llvm/llvm-project/pull/89425