Memtest86+ 1.50 builds and works perfectly on amd64 so it should have a amd64 keyword. I didn't try any earlier version.
Created attachment 50911 [details] Compile log. Attatched is the compile log. Also this is my emerge info: Portage 2.0.51-r15 (default-linux/amd64/2004.3, gcc-3.4.3, glibc-2.3.4.20040808-r1, 2.6.10-ck5 x86_64) ================================================================= System uname: 2.6.10-ck5 x86_64 AMD Athlon(tm) 64 Processor 3500+ Gentoo Base System version 1.4.16 Python: dev-lang/python-2.3.4 [2.3.4 (#1, Jan 26 2005, 16:31:09)] dev-lang/python: 2.3.4 sys-devel/autoconf: 2.59-r5 sys-devel/automake: 1.8.5-r1 sys-devel/binutils: 2.15.92.0.2-r2 sys-devel/libtool: 1.5.2-r7 virtual/os-headers: 2.6.8.1-r2 ACCEPT_KEYWORDS="amd64 ~amd64" AUTOCLEAN="yes" CFLAGS="-O2 -march=athlon64 -pipe" CHOST="x86_64-pc-linux-gnu" CONFIG_PROTECT="/etc /usr/kde/2/share/config /usr/kde/3.3/env /usr/kde/3.3/share/config /usr/kde/3.3/shutdown /usr/kde/3/share/config /usr/lib/X11/xkb /usr/share/config /var/qmail/control" CONFIG_PROTECT_MASK="/etc/gconf /etc/terminfo /etc/env.d" CXXFLAGS="-O2 -march=athlon64 -pipe" DISTDIR="/usr/portage/distfiles" FEATURES="autoaddcvs autoconfig ccache distlocks sandbox" GENTOO_MIRRORS="http://mirror.pudas.net/gentoo ftp://ftp.rhnet.is/pub/gentoo/ ftp://linux.rz.ruhr-uni-bochum.de/gentoo-mirror/ http://ftp.rhnet.is/pub/gentoo/" LANG="sv_SE.ISO8859-1" LC_ALL="sv_SE.ISO8859-1" MAKEOPTS="-j2" PKGDIR="/usr/portage/packages" PORTAGE_TMPDIR="/var/tmp" PORTDIR="/usr/portage" PORTDIR_OVERLAY="/usr/local/portage" SYNC="rsync://rsync.gentoo.org/gentoo-portage" USE="amd64 X aalib acpi alsa artswrappersuid berkdb bitmap-fonts caps cdr crypt dga dvd dvdr dvdread eds f77 fam fbcon flac font-server fortran gif gphoto2 gpm gtk gtk2 hal ipv6 jack jack-tmpfs java javascript jp2 jpeg kde lzw lzw-tiff mad mikmod mng motif mozilla mpeg multilib ncurses nls nptl nptlonly nvidia objc offensive oggvorbis opengl pam perl pic png pnp python qt quicktime readline real samba ssl svg tcpd tiff truetype truetype-fonts type1-fonts unicode usb userlocales vidix xine xml xml2 xmms xpm xrandr xv xvid zlib video_cards_nvidia linguas_sv" Unset: ASFLAGS, CBUILD, CTARGET, LDFLAGS
keyword added, thanks for your report.