[iOS] Always pass "-ObjC" when linking iOS executables.

build/config/ios/rules.gni

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/mac/base_rules.gni")
 
 # Generates Info.plist files for Mac apps and frameworks.
 #
 # Arguments
 #
@@ skipping 123 matching lines @@
                              "output_name",
                              "product_type",
                              "visibility",
                            ])
 
     output_name = rebase_path("$target_gen_dir/$_output_name", root_out_dir)
     if (!defined(libs)) {
       libs = []
     }
     libs += [ "UIKit.framework" ]
+    if (!defined(ldflags)) {
+      ldflags = []
+    }
+    ldflags += [ "-ObjC" ]
   }
 
   bundle_data(_bundle_data_executable) {
     forward_variables_from(invoker, [ "testonly" ])
     visibility = [ ":$_target_name" ]
     sources = [
       "$target_gen_dir/$_output_name",
     ]
     outputs = [
       "{{bundle_executable_dir}}/$_output_name",
@@ skipping 339 matching lines @@
                              [
                                "testonly",
                                "visibility",
                              ])
       public_deps = [
         ":$_framework_target+link",
       ]
     }
   }
 }