This mounts a new tmpfs on /tmp so any files residing there would be hidden
from the sandbox. Many programs store some files in there that might be useful
to an attacker. It also drops all capabilities incase it is ever run with
extra capabilities for whatever reason.
On some machines (like mine), `/proc` has to be mounted. Also, since
sandboxing with bubblewrap is best effort and assumes that an attacker doesn't
have control outside of the file to clean, it's safe to __try__ to enable some
bubblewrap features, and to silently fail otherwise.
without /etc/ld.so.cache available in the sandbox, tests fail on gentoo with:
/usr/bin/ffmpeg: error while loading shared libraries: libstdc++.so.6:
cannot open shared object file: No such file or directory
