Created attachment 202875 [details] patch Set/define GCC_BUILD_ONLY option to do not add gcc to RUN_DEPENDS. Some ports needs gcc to build, but can run witout installed gcc, for example math/mprime.
Earlier work: https://reviews.freebsd.org/D7223
https://reviews.freebsd.org/D7223 is better
I had to clean up and update a number of other things in the past months (and not too much time), but this is now my next area of attention, so I hope to land a solution for this -- based on https://reviews.freebsd.org/D7223 in the next week or so.