Add a [rtc_]build_with_neon variable to unify conditions.

webrtc/build/arm_neon.gypi

Index: webrtc/build/arm_neon.gypi
diff --git a/webrtc/build/arm_neon.gypi b/webrtc/build/arm_neon.gypi
index 9d8f71c8b12fb5e140479b8276df55b70f5bd085..9070080fc3af6dd1a67102f0a6b943fc513393e0 100644
--- a/webrtc/build/arm_neon.gypi
+++ b/webrtc/build/arm_neon.gypi
@@ -24,11 +24,19 @@
     '-mfpu=vfpv3-d16',
   ],
   'conditions': [
-    # "-mfpu=neon" is not requried for arm64 in GCC.
+    # "-mfpu=neon" is not required for arm64 in GCC.
     ['target_arch!="arm64"', {
       'cflags': [
         '-mfpu=neon',
        ],
     }],
+    # Disable LTO on NEON targets due to compiler bug.
+    # TODO(fdegans): Enable this. See crbug.com/408997.
+    ['use_lto==1', {
+      'cflags!': [
+        '-flto',
+        '-ffat-lto-objects',
+      ],
+    }],
   ],
 }