Update build tag constraints

This patch updates all build tag constraints to add the new format,
alongside the old one, to maintain backwards compatibility.

This was done by using `go fmt`.

See https://go.dev/doc/go1.17#gofmt and
https://golang.org/design/draft-gobuild for more details.

test/util/gocovcat.go

@@ -2,6 +2,7 @@
 //
 // From: https://git.lukeshu.com/go/cmd/gocovcat/
 //
+//go:build ignore
 // +build ignore
 
 // Copyright 2017 Luke Shumaker <lukeshu@parabola.nu>