[lld] [llvm] [LLVM][LTO] Factor out RTLib calls and allow them to be dropped (PR #98512)

[Joseph Huber via llvm-commits]

jhuber6 wrote:

> > Do you have a specific one in mind? I don't know of any cases where the backend renames a libcall that we can trigger.
> 
> Not really. Maybe setLibcallName(RTLIB::MEMMOVE, isPPC64 ? "___memmove64" : "___memmove");

Oh yeah, this patch doesn't do that yet because the runtimes still rename them later on in the pipeline. The first step I figured was just knowing which ones were disabled. I think a separate patch will need to pull that logic out as well, but I was hesitant because there's a lot of them and some of them depend on subtarget features. 

https://github.com/llvm/llvm-project/pull/98512