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

[Matt Arsenault via llvm-commits]

arsenm 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");

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