[lld] [LLD] [MinGW] Handle the --dll option (PR #68575)

[Markus Böck via llvm-commits]

https://github.com/zero9178 approved this pull request.

LGTM

Given that LDs doc say that it is basically equal to using `-shared` and that that is the only way users should use it, implementing implementation details of LD doesn't make sense to me unless really really often used in the wild.

https://github.com/llvm/llvm-project/pull/68575