[lld] [LLD] [MinGW] Interpret an empty -entry option as no entry point (PR #96055)

[via llvm-commits]

alvinhochun wrote:

> Also treat a missing -entry argument as no entry point; this also is what GNU ld does in this case.

Not sure if this is necessary or correct. Wouldn't this break the default entry points (e.g. `WinMainCRTStartup`/`mainCRTStartup`)?

https://github.com/llvm/llvm-project/pull/96055