patch from chinmaygarde@ to make progress on mac, ios.

build/config/ios/BUILD.gn

 # Copyright 2014 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/sysroot.gni")
 import("//build/config/ios/ios_sdk.gni")
 
 config("sdk") {
-  common_flags = [
-    "-isysroot",
-    sysroot,
-  ]
-
-  if (use_ios_simulator) {
-    common_flags += [ "-mios-simulator-version-min=$ios_deployment_target" ]
-  } else {
-    common_flags += [ "-miphoneos-version-min=$ios_deployment_target" ]
-  }
-
-  cflags = common_flags
-  ldflags = common_flags
 }