With Qt 5.12, standarddir.runtime() gives us a path in /private/var/folders/...
instead of /var/folders/... like before. Due to that change, the path length is
105 chars, which is too long for a named socket (104 seems to be okay).
The complete name is just slightly too long, so using i- instead of ipc- fixes
things...
Fixes#4471
See #888