libwebp: cherry-pick non-Xcode clang (iOS) build fix

third_party/libwebp/dsp/enc_neon.c

 // Copyright 2012 Google Inc. All Rights Reserved.
 //
 // Use of this source code is governed by a BSD-style license
 // that can be found in the COPYING 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.
 // -----------------------------------------------------------------------------
 //
 // ARM NEON version of speed-critical encoding functions.
@@ skipping 995 matching lines @@
   { 18, 19, 24, 25, 26, 27, 20, 21 },
   { 14, 15, 22, 23, 28, 29, 30, 31 }
 };
 
 static int QuantizeBlock(int16_t in[16], int16_t out[16],
                          const VP8Matrix* const mtx) {
   const int16x8_t out0 = Quantize(in, mtx, 0);
   const int16x8_t out1 = Quantize(in, mtx, 8);
   uint8x8x4_t shuffles;
   // vtbl4_u8 is marked unavailable for iOS arm64, use wider versions there.
-#if defined(__APPLE__) && defined(__aarch64__)
+#if defined(__APPLE__) && defined(__aarch64__) && \
+    defined(__apple_build_version__)

[fbarchard, 2014/12/11 18:00:58]

curious what this tests?  maybe worth a comment

   uint8x16x2_t all_out;
   INIT_VECTOR2(all_out, vreinterpretq_u8_s16(out0), vreinterpretq_u8_s16(out1));
   INIT_VECTOR4(shuffles,
                vtbl2q_u8(all_out, vld1_u8(kShuffles[0])),
                vtbl2q_u8(all_out, vld1_u8(kShuffles[1])),
                vtbl2q_u8(all_out, vld1_u8(kShuffles[2])),
                vtbl2q_u8(all_out, vld1_u8(kShuffles[3])));
 #else
   uint8x8x4_t all_out;
   INIT_VECTOR4(all_out,
@@ skipping 41 matching lines @@
   VP8CollectHistogram = CollectHistogram;
   VP8SSE16x16 = SSE16x16;
   VP8SSE16x8 = SSE16x8;
   VP8SSE8x8 = SSE8x8;
   VP8SSE4x4 = SSE4x4;
 #if !defined(WORK_AROUND_GCC)
   VP8EncQuantizeBlock = QuantizeBlock;
 #endif
 #endif   // WEBP_USE_NEON
 }