[lld] [LLD] [COFF] Warn if the runtime pseudo relocation function is missing (PR #88573)

[Keno Fischer via llvm-commits]

Keno wrote:

> Alternatively, we could also make this situation a hard error.

I think a hard error is probably better since non-application of the pseudo relocation ends up exposing the wrong symbol address. I think the situation would be different if the pseudo relocations where still being applied if the library was ultimately opened by an application that is linked against the mingw runtime, but that's not the case - the only question is whether the startup files are linked into the .dll, which we can detect here.

https://github.com/llvm/llvm-project/pull/88573