Show HN: Mgo: build a single Go binary optimized for all GOAMD64 variants

mgo builds the same program once for each GOAMD64 variant, and then bundles all of them with a launcher that at runtime picks the correct one for the local system. Handy if you have CPU-heavy workloads, but you can't assume which processor they run on; we use it in our kubernetes workloads to reduce CPU usage by ~3%.