Based on a patch by Erich E. Hoover.
Wine Staging has been carrying this code around since 2014. It should be fine to upstream it even if the rest of the [junction point patches](https://gitlab.winehq.org/wine/wine-staging/-/tree/master/patches/ntdll-Junc...) aren't ready yet, and upstreaming will reduce the burden on the Staging maintainers.