Add x86_64-pc-windows-msvc linker-plugin-lto instructions
I had some trouble getting cross language LTO working for this target, in part because the very few links of documentation I could find were linux-centric and because of a few very specific errors I ran into. I'm not sure if this is the correct place to document this, but this is one of the first links I found when looking for documentation so it might be the best place for it.