A previous (and already applied) patch added -static-libgcc to the plugin build flags, because they must not depend on a shared libgcc. But newer MinGW GCC builds now also default to a shared libstdc++, so plugins now also require -static-libstdc++.
Without this patch, C++ plugins such as NSISdl fail to load, see: https://bugzilla.redhat.com/show_bug.cgi?id=734905
The patch compiles (and -static-libstdc++ gets used correctly according to the build.log) on Fedora Rawhide.
nsis-2.46-static-libstdc++.patch