optimize the code

Author: LuuuXXX

src/bootstrap/builder.rs

@@ -302,15 +302,14 @@ impl StepDescription {
         }
     }
 
-    fn maybe_run(&self, builder: &Builder<'_>, pathsets: Vec<PathSet>) {
-        let excluded_pathsets: Vec<PathSet> = 
-            pathsets.iter().filter(|set| !self.is_excluded(builder, set)).cloned().collect();
+    fn maybe_run(&self, builder: &Builder<'_>, mut pathsets: Vec<PathSet>) {
+        pathsets.retain(|set| !self.is_excluded(builder, set));
 
         // Determine the targets participating in this rule.
         let targets = if self.only_hosts { &builder.hosts } else { &builder.targets };
 
         for target in targets {
-            let run = RunConfig { builder, paths: excluded_pathsets.clone(), target: *target };
+            let run = RunConfig { builder, paths: pathsets.clone(), target: *target };
             (self.make_run)(run);
         }
     }