As an aside, I think you only reason we needed multilib was so that we
could also compile nsis in when doing win64.
Not sure if that is still a limitation with newer versions.
If I get a chance I will take a look at gcc and nsis as well.
I played around with it a little and see the same you are seeing with the
incompatible thread line search.
Removing the links and similar efforts either lead to gcc not finding other
files, or still incompatible threads.
Removing multilib however does compile gcc ok.