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

[Matt Arsenault via llvm-commits]

https://github.com/arsenm commented:

This does fix a bug where LTO mishandles backends that rename libcalls from the default. Might be worth adding a test that shows that? 

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