fix compilation with gcc 4.6

src/bootstrapper.cc

Index: src/bootstrapper.cc
diff --git a/src/bootstrapper.cc b/src/bootstrapper.cc
index e9bb4eaf64b7524f82b2bc17e2e19d6a82146189..4f7cf409404e9e909aaa0bde8d36fd3b139acccf 100644
--- a/src/bootstrapper.cc
+++ b/src/bootstrapper.cc
@@ -1198,10 +1198,9 @@ void Genesis::InitializeExperimentalGlobal() {
   // TODO(mstarzinger): Move this into Genesis::InitializeGlobal once we no
   // longer need to live behind a flag, so WeakMap gets added to the snapshot.
   if (FLAG_harmony_weakmaps) {  // -- W e a k M a p
-    Handle<JSFunction> weakmap_fun =
-        InstallFunction(global, "WeakMap", JS_WEAK_MAP_TYPE, JSWeakMap::kSize,
-                        isolate->initial_object_prototype(),
-                        Builtins::kIllegal, true);
+    InstallFunction(global, "WeakMap", JS_WEAK_MAP_TYPE, JSWeakMap::kSize,
+                    isolate->initial_object_prototype(),
+                    Builtins::kIllegal, true);
   }
 }