Fix SDCH compile error on Mac GN bots.

sdch/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.
 
 config("sdch_config") {
   include_dirs = [ "open-vcdiff/src" ]
 }
 
 static_library("sdch") {
   sources = [
@@ skipping 49 matching lines @@
     }
   }
   configs += [ ":sdch_warnings" ]
 
   if (is_linux || is_android) {
     include_dirs = [ "linux" ]
   } else if (is_ios) {
     include_dirs = [ "ios" ]
   } else if (is_mac) {
     include_dirs = [ "mac" ]
+    defines = [ "OPEN_VCDIFF_USE_AUTO_PTR" ]
   } else if (is_win) {
     include_dirs = [ "win" ]
   }
 
   # open-vcdiff's logging.h introduces static initializers. This was
   # reported upstream years ago (
   # https://github.com/google/open-vcdiff/issues/33 ). Since
   # upstream won't fix this, work around it on the chromium side:
   # Inject a header that forwards to base/logging.h instead (which doesn't
   # introduce static initializers, and which prevents open-vcdiff's
   # logging.h from being used).
   if (is_win) {
     cflags = [
       "/FI",
       "sdch/logging_forward.h",
     ]
   } else {
     logging_file = rebase_path("logging_forward.h", root_build_dir)
     cflags = [
       "-include",
       logging_file,
     ]
   }
 }