zero out the build id for reproducible builds

We have been having issues with making builds reproducible, especially
with the `.note.go.buildid` ELF section. One tip from a golang issue was
to set `-ldflags=-buildid=` which seems to work well. You can confirm
that the buildid is set to empty by inspecting the binaries with the go
command example `go tool buildid _output/local/go/bin/kubectl`

Signed-off-by: Davanum Srinivas <[email protected]>

Author: dims

hack/lib/golang.sh

@@ -784,7 +784,7 @@ kube::golang::build_binaries() {
     # Disable SC2153 for this, as it will throw a warning that the local
     # variable goldflags will exist, and it suggest changing it to this.
     # shellcheck disable=SC2153
-    goldflags="${GOLDFLAGS=-s -w} $(kube::version::ldflags)"
+    goldflags="${GOLDFLAGS=-s -w -buildid=} $(kube::version::ldflags)"
     goasmflags="-trimpath=${KUBE_ROOT}"
     gogcflags="${GOGCFLAGS:-} -trimpath=${KUBE_ROOT}"