Add stub for avx.

src/opts/SkBlend_opts.h

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 /*
 ninja -C out/Release dm nanobench ; and ./out/Release/dm --match Blend_opts ; and ./out/Release/nanobench  --samples 300 --nompd --match LinearSrcOver -q
  */
 
 #ifndef SkBlend_opts_DEFINED
 #define SkBlend_opts_DEFINED
 
 #include "SkNx.h"
 #include "SkPM4fPriv.h"
 
+#if SK_CPU_SSE_LEVEL >= SK_CPU_SSE_LEVEL_SSE2
+    #include <immintrin.h>
+#endif
+
 namespace SK_OPTS_NS {
 
 // An implementation of SrcOver from bytes to bytes in linear space that takes advantage of the
 // observation that the 255's cancel.
 //    invA = 1 - (As / 255);
 //
 //    R = 255 * sqrt((Rs/255)^2 + (Rd/255)^2 * invA)
 // => R = 255 * sqrt((Rs^2 + Rd^2 * invA)/255^2)
 // => R = sqrt(Rs^2 + Rd^2 * invA)
 static inline void blend_srgb_srgb_1(uint32_t* dst, const uint32_t pixel) {
@@ skipping 213 matching lines @@
     void srcover_srgb_srgb(
         uint32_t* dst, const uint32_t* const src, int ndst, const int nsrc) {
         trivial_srcover_srgb_srgb(dst, src, ndst, nsrc);
     }
 
 #endif
 
 }  // namespace SK_OPTS_NS
 
 #endif//SkBlend_opts_DEFINED