"-o3" Он вообще для чего-нибудь нужен?

Засовываем в /etc/portage/bashrc примерно следующее:

#!/bin/sh                            
# /etc/portage/bashrc                

if [ "$0" = "/usr/lib/portage/bin/ebuild.sh" ]; then
 
  eecho() {
      echo -ne ' \e[1;36m*\e[0m '
      echo "$*"
  }

   case "$*"  in
      # stay really quiet here.
      depend) : ;;
      *)
         if [ -e ${ROOT}/etc/portage/package.cflags ]; then
            save_IFS
            IFS=$'\n'
            for x in $(/bin/cat ${ROOT}/etc/portage/package.cflags); do
               unset IFS
               x="$(echo $x)"
               IFS=$'\n'
               if [ "${x:0:1}" != "#" ]; then
                  PKG="${x%%[$'\t\n ']*}"
                  if [ "$PKG" == "$CATEGORY/$PN" ]; then

                     if [ "$CFLAGS" != "${x/$PKG/}" ]; then
                        eecho "Using package.cflags entry for $CATEGORY/$PN"
                     fi
                     export CFLAGS="${x/$PKG/}"
                     export CXXFLAGS="${x/$PKG/}"

                  fi
               fi
            done
            restore_IFS
         fi

      ;;
   esac
fi

======================================================

Далее chmod +x /etc/portage/bashrc и в /etc/portage/package.cflags забиваем необходимые пакеты\флаги компиляции, примерно так:

x11-libs/cairo -s -O2 -march=native -pipe
dev-libs/glib  -s -O2 -march=native -pipe
dev-db/sqlite  -s -O3 -march=native -pipe

Радуемся!

CFLAGS="-O3 -pipe -march=native -mtune=native -mfpmath=sse -floop-interchange -floop-strip-mine -floop-block"
CXXFLAGS="-O3 -pipe -march=native -mtune=native -mfpmath=sse -floop-interchange -floop-strip-mine -floop-block"
LDFLAGS="-Wl,--as-needed -Wl,--sort-common -Wl,-O1 -Wl,--hash-style=gnu"