This lets you build without TCG (hardware accelerationor qtest only).  When
this flag is passed to configure, it will automatically filter out the target
list to only those that support KVM or Xen or HAX.
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>