release/dist: add helper to build Go binaries with custom tags

Updates tailscale/corp#12861

Signed-off-by: David Anderson <danderson@tailscale.com>

release/dist/dist.go

@@ -184,6 +184,17 @@ func (b *Build) TmpDir() string {
 // binary. Builds are cached by path and env, so each build only happens once
 // per process execution.
 func (b *Build) BuildGoBinary(path string, env map[string]string) (string, error) {
+	return b.BuildGoBinaryWithTags(path, env, nil)
+}
+
+// BuildGoBinaryWithTags builds the Go binary at path and returns the
+// path to the binary. Builds are cached by path, env and tags, so
+// each build only happens once per process execution.
+//
+// The passed in tags override gocross's automatic selection of build
+// tags, so you will have to figure out and specify all the tags
+// relevant to your build.
+func (b *Build) BuildGoBinaryWithTags(path string, env map[string]string, tags []string) (string, error) {
 	err := b.Once("init-go", func() error {
 		log.Printf("Initializing Go toolchain")
 		// If the build is using a tool/go, it may need to download a toolchain
@@ -197,7 +208,7 @@ func (b *Build) BuildGoBinary(path string, env map[string]string) (string, error
 		return "", err
 	}
 
-	buildKey := []any{"go-build", path, env}
+	buildKey := []any{"go-build", path, env, tags}
 	return b.goBuilds.Do(buildKey, func() (string, error) {
 		b.goBuildLimit <- struct{}{}
 		defer func() { <-b.goBuildLimit }()
@@ -207,9 +218,17 @@ func (b *Build) BuildGoBinary(path string, env map[string]string) (string, error
 			envStrs = append(envStrs, k+"="+v)
 		}
 		sort.Strings(envStrs)
-		log.Printf("Building %s (with env %s)", path, strings.Join(envStrs, " "))
 		buildDir := b.TmpDir()
-		cmd := b.Command(b.Repo, b.Go, "build", "-v", "-o", buildDir, path)
+		args := []string{"build", "-v", "-o", buildDir}
+		if len(tags) > 0 {
+			tagsStr := strings.Join(tags, ",")
+			log.Printf("Building %s (with env %s, tags %s)", path, strings.Join(envStrs, " "), tagsStr)
+			args = append(args, "-tags="+tagsStr)
+		} else {
+			log.Printf("Building %s (with env %s)", path, strings.Join(envStrs, " "))
+		}
+		args = append(args, path)
+		cmd := b.Command(b.Repo, b.Go, args...)
 		for k, v := range env {
 			cmd.Cmd.Env = append(cmd.Cmd.Env, k+"="+v)
 		}