This allows executables to be found by :!, system(), and executable() if they live next to ("sibling" to) nvim.exe. This is what gvim on Windows does, and also matches the behavior of Win32 SearchPath(). c4a249a736/src/os_win32.c (L354-L370)
c4a249a736/src/os_win32.c (L354-L370)