Remove runtime NEON detection

webrtc/build/webrtc.gni

 # Copyright (c) 2014 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.
 
 import("//build/config/arm.gni")
 import("//build/config/features.gni")
@@ skipping 60 matching lines @@
   # TODO(ljubomir): Unset rtc_use_openmax_dl for mips64el once mips64el gets
   # supported in GN (since openmax_dl is not supported for mips64el).
   if (!is_ios && (current_cpu != "arm" || arm_version >= 7)) {
     rtc_use_openmax_dl = true
   } else {
     rtc_use_openmax_dl = false
   }
 
   # Determines whether NEON code will be built.
   rtc_build_with_neon =
-      (current_cpu == "arm" && (arm_use_neon || arm_optionally_use_neon)) ||
-      current_cpu == "arm64"
+      (current_cpu == "arm" && arm_use_neon) || current_cpu == "arm64"
 
   # Enable this to use HW H.264 encoder/decoder on iOS PeerConnections.
   # Enabling this may break interop with Android clients that support H264.
   rtc_use_objc_h264 = false
 
   # Enable this to build OpenH264 encoder/FFmpeg decoder. This is supported on
   # all platforms except Android and iOS. Because FFmpeg can be built
   # with/without H.264 support, |ffmpeg_branding| has to separately be set to a
   # value that includes H.264, for example "Chrome". If FFmpeg is built without
   # H.264, compilation succeeds but |H264DecoderImpl| fails to initialize. See
@@ skipping 16 matching lines @@
 declare_args() {
   # Include the iLBC audio codec?
   rtc_include_ilbc = !(build_with_chromium || build_with_mozilla)
 }
 
 # Make it possible to provide custom locations for some libraries (move these
 # up into declare_args should we need to actually use them for the GN build).
 rtc_libvpx_dir = "//third_party/libvpx"
 rtc_libyuv_dir = "//third_party/libyuv"
 rtc_opus_dir = "//third_party/opus"