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

[Sam Clegg via llvm-commits]

https://github.com/sbc100 commented:

Can you explain what you mean by "but cannot maintain the overhead
of several unused function calls"? 

My understanding is that these symbols are still only included in the final binary if they are actually required/referenced.    The `handleLibcall` mechanism just forces them to be included/available during LTO compilation, it doesn't actually force them to be included in the output binary, does it?

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