Make libusb deprecation warning go away on OSX 10.12.

third_party/libusb/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.
 
 assert(!is_android && !is_ios)
 
 import("//build/config/features.gni")
 
 config("libusb_config") {
   include_dirs = [ "src/libusb" ]
@@ skipping 62 matching lines @@
       "HAVE_GETTIMEOFDAY=1",
       "HAVE_POLL_H=1",
       "HAVE_SYS_TIME_H=1",
       "LIBUSB_DESCRIBE=\"1.0.16\"",
       "POLL_NFDS_TYPE=nfds_t",
       "THREADS_POSIX=1",
     ]
   }
 
   if (is_mac) {
-    defines += [ "OS_DARWIN=1" ]
+    defines += [
+      "OS_DARWIN=1",
+
+      # Needed on OSX 10.12 to silence a deprecation warning.
+      "OBJC_SILENCE_GC_DEPRECATIONS=1",
+    ]
   } else {
     sources -= [
       "src/libusb/os/darwin_usb.c",
       "src/libusb/os/darwin_usb.h",
     ]
   }
 
   if (is_linux) {
     sources += [
       "src/libusb/os/linux_usbfs.c",
@@ skipping 39 matching lines @@
       "src/libusb/os/threads_windows.h",
       "src/libusb/os/windows_common.h",
       "src/libusb/os/windows_usb.c",
       "src/libusb/os/windows_usb.h",
       "src/msvc/config.h",
       "src/msvc/inttypes.h",
       "src/msvc/stdint.h",
     ]
   }
 }