Fix compilation of uber-fat binaries.

build/config/ios/ios_sdk.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.
 
 declare_args() {
   # SDK path to use. When empty this will use the default SDK based on the
   # value of use_ios_simulator.
   ios_sdk_path = ""
   ios_sdk_name = ""
   ios_sdk_version = ""
   ios_sdk_platform = ""
   ios_sdk_platform_path = ""
   xcode_version = ""
   xcode_build = ""
   machine_os_build = ""
 
-  use_ios_simulator = current_cpu == "x86" || current_cpu == "x64"
-
   # Version of iOS that we're targeting.
   ios_deployment_target = "9.0"
 
   # The iOS Code signing identity to use
   # TODO(GYP), TODO(sdfresne): Consider having a separate
   # ios_enable_code_signing_flag=<bool> flag to make the invocation clearer.
   ios_enable_code_signing = true
   ios_code_signing_identity = ""
 
   # If non-empty, this list must contain valid cpu architecture, and the final
   # build will be a multi-architecture build (aka fat build) supporting the
   # main $target_cpu architecture and all of $additional_target_cpus.
   #
   # For example to build an application that will run on both arm64 and armv7
   # devices, you would use the following in args.gn file when running "gn args":
   #
   #   target_os = "ios"
   #   target_cpu = "arm64"
   #   additional_target_cpus = [ "arm" ]
   #
   # You can also pass the value via "--args" parameter for "gn gen" command by
   # using the syntax --args='additional_target_cpus=["arm"] target_cpu="arm64"'.
   additional_target_cpus = []
 }
 
 assert(custom_toolchain == "" || additional_target_cpus == [],
        "cannot define both custom_toolchain and additional_target_cpus")
 
+use_ios_simulator = current_cpu == "x86" || current_cpu == "x64"
+
 # Initialize additional_toolchains from additional_target_cpus. Assert here
 # that the list does not contains $target_cpu nor duplicates as this would
 # cause weird errors during the build.
 additional_toolchains = []
 if (additional_target_cpus != []) {
   foreach(_additional_target_cpu, additional_target_cpus) {
     assert(_additional_target_cpu != target_cpu,
            "target_cpu must not be listed in additional_target_cpus")
 
     _toolchain = "//build/toolchain/mac:ios_clang_$_additional_target_cpu"
@@ skipping 40 matching lines @@
     ios_code_signing_identity = _ios_identities[0]
   }
 
   if (ios_code_signing_identity == "") {
     print("Tried to prepare a device build without specifying a code signing")
     print("identity and could not detect one automatically either.")
     print("TIP: Simulator builds don't require code signing...")
     assert(false)
   }
 }