Add not_needed function

tools/gn/functions.h

Index: tools/gn/functions.h
diff --git a/tools/gn/functions.h b/tools/gn/functions.h
index 401384acbf30845a2b48eaeb6752abe1fa0d37c9..c09612c40de7b9b67fda7169e4fd394a09f58a9f 100644
--- a/tools/gn/functions.h
+++ b/tools/gn/functions.h
@@ -221,6 +221,14 @@ Value RunLoadableModule(Scope* scope,
                         BlockNode* block,
                         Err* err);
 
+extern const char kNotNeeded[];
+extern const char kNotNeeded_HelpShort[];
+extern const char kNotNeeded_Help[];
+Value RunNotNeeded(Scope* scope,
+                   const FunctionCallNode* function,
+                   const ListNode* args_list,
+                   Err* err);
+
 extern const char kPool[];
 extern const char kPool_HelpShort[];
 extern const char kPool_Help[];