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

[Petr Hosek via cfe-commits]

petrhosek wrote:

> Does it really needed?

It is, #89234 only covers compiler-rt but not other runtime libraries such as libc or libc++ so you might end up with the following:

```
lib/19/clang/lib/x86_64-unknown-linux-gnu/libclang_rt.builtins.a
lib/x86_64-linux-gnu/libc++.a
```

The driver will then fail to fine `libc++.a` leading to a link failure.

This change expand the normalization to cover all runtime libraries.

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