Add a [rtc_]build_with_neon variable to unify conditions.

webrtc/build/arm_neon.gypi

 # Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 # This file sets correct neon flags. Include it if you want to build
 # source with neon intrinsics.
@@ skipping 12 matching lines @@
   'cflags!': [
     '-mfpu=vfpv3-d16',
   ],
   'conditions': [
     # "-mfpu=neon" is not requried for arm64 in GCC.
     ['target_arch!="arm64"', {
       'cflags': [
         '-mfpu=neon',
        ],
     }],
+    # Disable LTO due to compiler bug.
+    ['use_lto==1', {
+      'cflags!': [
+        '-flto',
+        '-ffat-lto-objects',
+      ],
+    }],
   ],
 }