When launching a custom msys2 environment, and it does "first-run"
operations, it complains that: "cannot change permissions of
'/dev/shm': Permission denied".
This is related to the previous work in this area that happened
in #2337: Since "/" is mounted with noacl and chmod() is a no-op,
this error is cosmetic and can be removed.
However, in #2337, the access modifying behaviour was not removed
from the "mkdir" branch, which this patch aims to address.
9b03596ad6