The purpose of this commit is twofold; from the user's perspective, this
provides a consistent experience whenever building a sofort-based project;
and from the developer's perspective, this provides an easy way to test
cfgdefs.mk even before the writing and/or integration of cfgdefs.sh.
Special thanks to Jonas 'Sortie' Termansen, author of the Sortix operating
sys (https://sortix.org), for brainstorming about the best way to forward
arguments containing special symbols or characters to a sourced (aka dot)
shell script, as well as sharing single-quote tips and tricks.
