My deliverable is source code; my code targets several different platforms; and my clients expect to produce builds for all supported platforms from one build e

My deliverable is source code; my code targets several different platforms; and my clients expect to produce builds for all supported platforms from one build environment. Delivering with GNU Make alone would require me to either write tons of documentation for my clients to read in order to setup their build environment just right or write tons of shell script to accomplish a fraction of what GNU Autotools already does. I'll pre-emptively state that delivering a "use this to build" Docker image is not an option, unfortunately.