I've been testing wine with win64 use on a no-multilib profile and it builds OK. I attach a patch to be able to build wine.
Created attachment 190958 [details, diff] wine-1.1.21_no_multilib_win64.patch
simply doing "!win64? ( amd64? ( ......" should be sufficient
should be fixed in cvs now, thanks http://sources.gentoo.org/app-emulation/wine/wine-1.1.13.ebuild?r1=1.10&r2=1.11 http://sources.gentoo.org/app-emulation/wine/wine-1.1.14.ebuild?r1=1.5&r2=1.6 http://sources.gentoo.org/app-emulation/wine/wine-1.1.15.ebuild?r1=1.7&r2=1.8 http://sources.gentoo.org/app-emulation/wine/wine-1.1.16.ebuild?r1=1.6&r2=1.7 http://sources.gentoo.org/app-emulation/wine/wine-1.1.17.ebuild?r1=1.3&r2=1.4 http://sources.gentoo.org/app-emulation/wine/wine-1.1.18.ebuild?r1=1.3&r2=1.4 http://sources.gentoo.org/app-emulation/wine/wine-1.1.19.ebuild?r1=1.3&r2=1.4 http://sources.gentoo.org/app-emulation/wine/wine-1.1.20.ebuild?r1=1.3&r2=1.4 http://sources.gentoo.org/app-emulation/wine/wine-1.1.21.ebuild?r1=1.2&r2=1.3 http://sources.gentoo.org/app-emulation/wine/wine-9999.ebuild?r1=1.36&r2=1.37
alternatively you could >=add app-emulation/wine-1.1.13 win64 to package.use.force. That would be more logical to the user that emerges wine. you should also change app-emulation/wine to <app-emulation/wine-1.1.13 in package.mask
that is for the amd64 team to handle. feel free to suggest that *to them*.