[clang] [Clang] Automatically link the `compiler-rt` for GPUs if present (PR #109152)

[Joseph Huber via cfe-commits]

jhuber6 wrote:

> I'm not sure about this. What does `compiler-rt` provide?

It's `clang_rt.builtins`. So, basically complex number multiplication / division, wide integer stuff (I think the backend handles i128 now though). We currently have a wrapper header that defined `__mulsc3` for the device even though it's supposed to come from the compiler-rt.

https://github.com/llvm/llvm-project/pull/109152