build: don't rely on the order of dependencies

It is impossible to sanely keep things tracked like that. All common
algorithms work on unordered graphs, and now we match that as well.

shell_helpers.py

@@ -261,7 +261,10 @@ class ShellHelpers:
     def rmrf(self, path):
         self.print_cmd(['rm', '-r', '-f', path, LF])
         if not self.dry_run and os.path.exists(path):
-            shutil.rmtree(path)
+            if os.path.isdir(path):
+                shutil.rmtree(path)
+            else:
+                os.unlink(path)
 
     def write_configs(self, config_path, configs, config_fragments=None):
         '''