more dynamic detection of stuff in config.mk

[ipelupessy]

Is your feature request related to a problem? Please describe.
config.mk is generated once at install time. Most of the stuff in there is only needed later at compile.

Describe the solution you'd like
a mechanism whereby detection proceeds at compile time (or maybe a possibility of regenerating it w/o reinstall)

Describe alternatives you've considered
telling everyone to reinstall if the environment is updated

Additional context
clearly this needs some thought...

[rieder]

Yeah that sounds like the right mechanism. The alternative mentioned is what we have now and it isn't great.
Another alternative could be having individual config.mk files for each package.

[ipelupessy]

see #583