> nothing ever sets BROKEN_TOUPPER

Even in the original Vim source before neovim's fork? neovim removed all the Windows support (I guess because libuv will handle it), but these defines very well could have been erroneously removed. It's happened twice before... ([FEAT_SIGNS](https://github.com/neovim/neovim/issues/383) and [FEAT_FILTERPIPE](https://github.com/neovim/neovim/pull/413))