[ci] Expand build job suite to span space of compilation options

Task is to create a CI build job template under the build stage, and then have a number of parallel build jobs that test various compilation options controlled via environment variables as listed in setup.sh:

https://gitlab.cern.ch/cms_tk_ph2/Ph2_ACF/-/blob/Dev/setup.sh#L103-125

This is distinct from #34 (closed), but should eventually be built such that the OR of the warnings from these jobs is published to the system described there.

For now, this is a simple addition of jobs to the build stage with a before_script that changes the environment variables.