net-im/libsignal-node: Fix poudriere build

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

Approved by: mikael (maintainer)
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D46966