build: Actually set build tags (#6866)

Apparently our Tags field depended on having specific files react to
tags and add themselves there. This, instead, works for all tags.

Also, pass tags to the test command line.

lib/build/build.go

@@ -12,6 +12,7 @@ import (
 	"os"
 	"regexp"
 	"runtime"
+	"sort"
 	"strconv"
 	"strings"
 	"time"
@@ -23,6 +24,7 @@ var (
 	Host    = "unknown"
 	User    = "unknown"
 	Stamp   = "0"
+	Tags    = ""
 
 	// Static
 	Codename = "Fermium Flea"
@@ -34,9 +36,6 @@ var (
 	IsBeta      bool
 	LongVersion string
 
-	// Set by Go build tags
-	Tags []string
-
 	allowedVersionExp = regexp.MustCompile(`^v\d+\.\d+\.\d+(-[a-z0-9]+)*(\.\d+)*(\+\d+-g[0-9a-f]+)?(-[^\s]+)?$`)
 
 	envTags = []string{
@@ -88,13 +87,19 @@ func LongVersionFor(program string) string {
 	// This string and date format is essentially part of our external API. Never change it.
 	date := Date.UTC().Format("2006-01-02 15:04:05 MST")
 	v := fmt.Sprintf(`%s %s "%s" (%s %s-%s) %s@%s %s`, program, Version, Codename, runtime.Version(), runtime.GOOS, runtime.GOARCH, User, Host, date)
+
+	tags := strings.Split(Tags, ",")
+	if len(tags) == 1 && tags[0] == "" {
+		tags = tags[:0]
+	}
 	for _, envVar := range envTags {
 		if os.Getenv(envVar) != "" {
-			Tags = append(Tags, strings.ToLower(envVar))
+			tags = append(tags, strings.ToLower(envVar))
 		}
 	}
-	if len(Tags) > 0 {
-		v = fmt.Sprintf("%s [%s]", v, strings.Join(Tags, ", "))
+	if len(tags) > 0 {
+		sort.Strings(tags)
+		v = fmt.Sprintf("%s [%s]", v, strings.Join(tags, ", "))
 	}
 	return v
 }