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 cros_boot_mode` passes now

Change-Id: Icd33e60bd26c29089c2905e914e6998a3d6611b2
Reviewed-on: https://gerrit.chromium.org/gerrit/11850
Reviewed-by: Ben Chan <benchan@chromium.org>
Commit-Ready: Matt Tennant <mtennant@chromium.org>
Tested-by: Matt Tennant <mtennant@chromium.org>
1 file changed