Update mig.py to take an explicit sdk argument.

build/secondary/third_party/crashpad/crashpad/util/BUILD.gn

 # 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/toolchain/toolchain.gni")
 
 if (is_mac) {
   import("//build/config/sysroot.gni")
 }
 
@@ skipping 17 matching lines @@
     outputs = [
       "$target_gen_dir/mach/{{source_name_part}}User.c",
       "$target_gen_dir/mach/{{source_name_part}}Server.c",
       "$target_gen_dir/mach/{{source_name_part}}.h",
       "$target_gen_dir/mach/{{source_name_part}}Server.h",
     ]
 
     args = [ "{{source}}" ]
     args += rebase_path(outputs, root_build_dir)
     if (!use_system_xcode) {
-      args += [ hermetic_xcode_path ]
+      args += [
+        "--developer-dir",
+        hermetic_xcode_path,
+      ]
     }
+    args += [
+      "--sdk",
+      mac_sdk_path,
+    ]
   }
 }
 
 static_library("util") {
   sources = [
     "file/file_io.cc",
     "file/file_io.h",
     "file/file_io_posix.cc",
     "file/file_io_win.cc",
     "file/file_reader.cc",
@@ skipping 193 matching lines @@
   } else if (is_mac) {
     sources += get_target_outputs(":mig")
     deps += [ ":mig" ]
     libs = [
       "CoreFoundation.framework",
       "Foundation.framework",
       "IOKit.framework",
     ]
   }
 }