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

[Joseph Huber via cfe-commits]

jhuber6 wrote:

> I like this direction and I think it should be the right way. However, IMHO, I think it needs discussion (and potentially an RFC).

Moving from the header to the definition in `compiler-rt` would warrant an RFC, this patch just automatically links something that exists and will only provide definitions if they are undefined. So the only effect this has right now is linking in a symbol that would otherwise be a linker error.

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