go build -a

Since most of us use the Dockerfile/Makefile to rebuild, this will change the actual build time for only a small handful of people, and not by much.  In return, we get _much_ more consistent builds, especially when running tests (which do a `go test -i`) and then building afterwards with GOPATH/pkg directories around (yes, this has bitten me several times, one of them very recent and prompting this change).