The wine ebuild uses the CFLAGS and CXXFLAGS form make.conf as many other ebuilds. That's a show-stopper though. Compiled with my "-mcpu=i686 -march=i686 -O3 -pipe" wine seems to be working at first but when I try to install programs wine complains about bad EXE files etc. Without the optimizations everything runs just fine. I suggest to make an unset CFLAGS and unset CXXFLAGS in the wine ebuild as I did in my portage tree.
OK, I've committed a new revision that unsets CFLAGS and CXXFLAGS prior to running configure.
For me, it caused misterious "can't exec starcraft.exe. error=21" at CFLAGS="-march=i686 -mcpu=i586 -O2", which is not that agressive at all.