[llvm] [Linker] Propagate `nobuiltin` attributes when linking known libcalls (PR #89431)

[Johannes Doerfert via llvm-commits]

https://github.com/jdoerfert requested changes to this pull request.

I don't think this works without a module flag because the user might switch the order; linking the application into libc, or linking something else later into the application with libc. Either way, we wouldn't link in libcalls but we already had them. Still we can't perform libcall reasoning on the new functions.

https://github.com/llvm/llvm-project/pull/89431