i didn't have CXXFLAGS defined in make.conf, but emerge --info shows: CFLAGS="-march=pentium3 -O2 -pipe" CXXFLAGS="-O2 -mcpu=i686 -pipe" these values could well be CFLAGS i used in the past, this installation is rather old.
Those are CXXFLAGS from profile and are just fine. If you dislike them, define your own.