Created attachment 440068 [details]
As can be deduced from the almost-completely-useless logs, build of dev-ruby/json failed for me trying to use no-longer-installed gcc version that I happened to have in CC when I rebuilt dev-lang/ruby last time. Which means it doesn't respect the current value of CC/CXX after all.
If this is a generic issue with Ruby packages, feel free to transform this bug into a generic one.
Created attachment 440070 [details]
Yes, this is a generic ruby extension built system issue. I think bug 476668 is related.