[LLD] [MinGW] Pass LLVM specific LTO options through to lld-link

This is modelled after how the ELF driver does it (see e.g.
https://reviews.llvm.org/D78158 for the source of the ELF
implementation); we need to intercept some options, but ignore GCC
specific ones that GCC passes regardless of whether GCC is using
LTO or not.

This is the second part of the fix for
https://github.com/mstorsjo/llvm-mingw/issues/349.

Differential Revision: https://reviews.llvm.org/D158412