After the update to 0.58.0, the port failed to build in poudriere during
the fetch phase, giving the error:
make: Could not create temporary file
/wrkdirs/usr/ports/net-im/libsignal-node/work/makekSsI9M: No such file
or directory
Instead of removing ${WRKDIR} in the pre-fetch phase, clearing its
contents resolves the issue and allows the build to succeed.