Move use_system_xcode to //build_overrides/build.gni

build_overrides/build.gni

 # Copyright 2016 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.
 
 # Several dependencies of Chrome require a different min sdk and/or deployment
 # target when built as stand-alone projects. If this is ever not the case, these
 # variables can be removed.
 # See https://bugs.chromium.org/p/webrtc/issues/detail?id=5453.
 mac_sdk_min_build_override = "10.10"
 mac_deployment_target_build_override = "10.9"
@@ skipping 19 matching lines @@
 tsan_suppressions_file = "//build/sanitizers/tsan_suppressions.cc"
 
 # Uncomment these to specify a different lint suppressions file for android
 # lint_suppressions_file = path/to/your/suppressions/file/suppressions.xml
 
 declare_args() {
   # Android 32-bit non-component, non-clang builds cannot have symbol_level=2
   # due to 4GiB file size limit, see https://crbug.com/648948.
   # Set this flag to true to skip the assertion.
   ignore_elf32_limitations = false
+
+  # Use the system install of Xcode for tools like ibtool, libtool, etc.
+  # This does not affect the compiler. When this variable is false, targets will
+  # instead use a hermetic install of Xcode. [The hermetic install can be
+  # obtained with gclient sync after setting the environment variable
+  # FORCE_MAC_TOOLCHAIN].
+  use_system_xcode = ""
 }
+
+if (use_system_xcode == "") {
+  if (target_os == "mac") {
+    _result =
+        exec_script("//build/mac/should_use_hermetic_xcode.py", [], "value")
+    use_system_xcode = _result == 0
+  }
+  if (target_os == "ios") {
+    use_system_xcode = true
+  }
+}