x86only: build no-kvm-by-default {x86_64,i386}-softmmu binaries, too
    
    This fixes two issues at the same time:
     - The qemu-system-x86_64 binary was not being built in the
       second configure+make run
     - The second configure+make run was not generating the qemu-img and
       qemu-io binaries because it didn't include any -softtmu target
    
    Those issues appeared only if x86only option was enabled, as the default
    $buildarch definition already included x86_64-softmmu and i386-softmmu.
    
    Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>