build: make go buildid static (#30342)

The previous clearing of buildid did fully work, turns out we need to
set it in `ldflags`

The go buildid is the only remaining hurdle for reproducible builds, see
ethereum/go-ethereum#28987 (comment)

This PR changes the go build id application note to say literally `none`

golang/go#33772 (comment):

> This difference is due to the .note.go.buildid section added by the
linker. It can be set to something static e.g. -ldflags=-buildid= (empty
string) to gain reproducibility.

build/ci.go

@@ -261,6 +261,10 @@ func doInstall(cmdline []string) {
 // buildFlags returns the go tool flags for building.
 func buildFlags(env build.Environment, staticLinking bool, buildTags []string) (flags []string) {
 	var ld []string
+	// See https://github.com/golang/go/issues/33772#issuecomment-528176001
+	// We need to set --buildid to the linker here, and also pass --build-id to the
+	// cgo-linker further down.
+	ld = append(ld, "--buildid=none")
 	if env.Commit != "" {
 		ld = append(ld, "-X", "main.gitCommit="+env.Commit)
 		ld = append(ld, "-X", "main.gitDate="+env.Date)