The performance gain will be marginal but looking after the problem if some port fails to compile will drives you crazy. Furthermore posting a PR with such 'optimizations' will not get you any response. This is in my opinion 'Gentooish behaviour'.
>But how can I recompile all the already installed ports to take this change in account?
As you can see, there are more important thing to learn instead of tinkering with the stability and reliability of the system
http://www.gsp.com/cgi-bin/man.cgi?s...ic=portupgrade