Add stub for avx.

src/core/SkOpts.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCpu.h"
 #include "SkHalf.h"
 #include "SkOnce.h"
@@ skipping 72 matching lines @@
             sk_default::color_xform_RGB1_2dot2_to_2dot2;
     decltype(color_xform_RGB1_srgb_to_srgb)   color_xform_RGB1_srgb_to_srgb   =
             sk_default::color_xform_RGB1_srgb_to_srgb;
     decltype(color_xform_RGB1_2dot2_to_srgb)  color_xform_RGB1_2dot2_to_srgb  =
             sk_default::color_xform_RGB1_2dot2_to_srgb;
 
     // Each Init_foo() is defined in src/opts/SkOpts_foo.cpp.
     void Init_ssse3();
     void Init_sse41();
     void Init_sse42() {}
-    void Init_avx() {}
+    void Init_avx();
     void Init_avx2() {}
 
     static void init() {
     #if defined(SK_CPU_X86) && !defined(SK_BUILD_NO_OPTS)
         if (SkCpu::Supports(SkCpu::SSSE3)) { Init_ssse3(); }
         if (SkCpu::Supports(SkCpu::SSE41)) { Init_sse41(); }
         if (SkCpu::Supports(SkCpu::SSE42)) { Init_sse42(); }
         if (SkCpu::Supports(SkCpu::AVX  )) { Init_avx();   }
         if (SkCpu::Supports(SkCpu::AVX2 )) { Init_avx2();  }
     #endif
     }
 
     void Init() {
         static SkOnce once;
         once(init);
     }
 }  // namespace SkOpts