Correct QEMU_ARCH to use x86_64 rather than amd64.

The default ARCH is not the qemu suffix needed on amd64.  This
maps amd64 to x86_64 for qemu executables.

BUG=chromium-os:22309
TEST=`sudo FEATURES="test" emerge-amd64-generic verity` passes now

Change-Id: I5bd98aa18ec6516e44ae2336e045d05af3bef6c6
Reviewed-on: https://gerrit.chromium.org/gerrit/11824
Tested-by: Matt Tennant <mtennant@chromium.org>
Reviewed-by: Anush Elangovan <anush@chromium.org>
Reviewed-by: Ben Chan <benchan@chromium.org>
Reviewed-by: Will Drewry <wad@chromium.org>
Commit-Ready: Matt Tennant <mtennant@chromium.org>
1 file changed