Dynamic MAKE_JOBS_NUMBER_LIMIT

[bob prohaska]

Is it possible to dynamically set MAKE_JOBS_NUMBER_LIMIT based on
swap usage? The idea would be to check swap usage and start new 
make jobs only when swap use is "low enough", on the Pi3 that
would be less than about 500 MB in my setup.

I've tried manually adjusting the number up during a long make
session (www/chromium) and it seemed to work, but only up. Going
from 2 to 3 got an extra c++ instance, but when the machine got
swap-bound setting it back to 2 didn't inhibit creation of new jobs..

Thanks for reading!

bob prohaska