RFE: Please implement -cpu best or a CPU fallback option

QEMU should implement a -cpu best option or some other way to make this work:

qemu -M pc,accel=kvm:tcg -cpu best

qemu -M pc,accel=kvm:tcg -cpu host:qemu64

See also:

https://bugzilla.redhat.com/show_bug.cgi?id=1277744#c6