[clang] [Driver,BareMetal] Replace -lclang_rt.builtins{,-$arch}.a with an absolute path (PR #82424)

[Petr Hosek via cfe-commits]

petrhosek wrote:

I agree with @MaskRay that prior to this change the BareMetal driver was using a logic that was inconsistent with all other drivers and not something we intend to support. The correct solution is to extend the BareMetal driver to support `multilib.yaml` for Clang runtime libraries; this includes not only compiler-rt builtins but also LLVM libc and libc++.

https://github.com/llvm/llvm-project/pull/82424