[lld] [LLD][MinGW] Fix implicit DLL entry point (PR #171680)

[Mateusz Mikuła via llvm-commits]

mati865 wrote:

A note for the reviewers: I hardly ever use C/C++ these days, so don't hesitate to point out if something can be done in a better way.

https://github.com/llvm/llvm-project/pull/171680