version: fix build version using buildInfo (#2789)

In go1.18 buildInfo will include the git revision hash, use that to fix
the Build field of Version so that it is correct even if Delve wasn't
built using make.go.

pkg/version/fixbuild.go

@@ -0,0 +1,23 @@
+//go:build go1.18
+// +build go1.18
+
+package version
+
+import "runtime/debug"
+
+func init() {
+	fixBuild = buildInfoFixBuild
+}
+
+func buildInfoFixBuild(v *Version) {
+	info, ok := debug.ReadBuildInfo()
+	if !ok {
+		return
+	}
+	for i := range info.Settings {
+		if info.Settings[i].Key == "gitrevision" {
+			v.Build = info.Settings[i].Value
+			break
+		}
+	}
+}

pkg/version/version.go

@@ -24,6 +24,7 @@ var (
 )
 
 func (v Version) String() string {
+	fixBuild(&v)
 	ver := fmt.Sprintf("Version: %s.%s.%s", v.Major, v.Minor, v.Patch)
 	if v.Metadata != "" {
 		ver += "-" + v.Metadata
@@ -38,3 +39,7 @@ var buildInfo = func() string {
 func BuildInfo() string {
 	return fmt.Sprintf("%s\n%s", runtime.Version(), buildInfo())
 }
+
+var fixBuild = func(v *Version) {
+	// does nothing
+}