Instead of deny build of QEMU without a default accelerator, simply
report an error when the user haven't passed -accel or -machine accel=
and TCG and KVM isn't builtin.
./configure already check that at least one accelerator is available.
Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>