Add a cross process build lock and use it in the archetype content builder

Fixes #9048

hugolib/hugo_sites_build.go

@@ -44,19 +44,17 @@ import (
 // Build builds all sites. If filesystem events are provided,
 // this is considered to be a potential partial rebuild.
 func (h *HugoSites) Build(config BuildCfg, events ...fsnotify.Event) error {
-	if h.running {
-		// Make sure we don't trigger rebuilds in parallel.
-		h.runningMu.Lock()
-		defer h.runningMu.Unlock()
-	} else {
-		defer func() {
-			h.Close()
-		}()
-	}
-
 	ctx, task := trace.NewTask(context.Background(), "Build")
 	defer task.End()
 
+	if !config.NoBuildLock {
+		unlock, err := h.BaseFs.LockBuild()
+		if err != nil {
+			return errors.Wrap(err, "failed to acquire a build lock")
+		}
+		defer unlock()
+	}
+
 	errCollector := h.StartErrorCollector()
 	errs := make(chan error)