Add stub for avx.

src/opts/SkOpts_avx.cpp

Index: src/opts/SkOpts_avx.cpp
diff --git a/src/core/SkSwizzle.cpp b/src/opts/SkOpts_avx.cpp
similarity index 56%
copy from src/core/SkSwizzle.cpp
copy to src/opts/SkOpts_avx.cpp
index f080b83a87870e5f2a528345b9585c90c74c955f..835e0c0ded9e505951187d379f1cf50bd51eaea4 100644
--- a/src/core/SkSwizzle.cpp
+++ b/src/opts/SkOpts_avx.cpp
@@ -5,10 +5,11 @@
  * found in the LICENSE file.
  */
 
-#include "SkSwizzle.h"
-
 #include "SkOpts.h"
 

[mtklein_C, 2016/06/22 20:33:41]

Looks like you should be including <immintrin.h> explicitly in SkBlend_opts.h.

SkNx doesn't necessarily include it for you, even on x86.  We have a build mode
where SkNx.h does not use SSE intrinsics on x86.  We like this bot as a control.

SkOpts_ssse3.cpp and SkOpts_sse41.cpp have been getting away with it because
they include other headers first that include <immintrin.h>.

I also don't mind if we just have each of SkOpts_{ssse3,sse41,avx} include
<immintrin.h>.

-void SkSwapRB(uint32_t* dest, const uint32_t* src, int count) {
-    SkOpts::RGBA_to_BGRA(dest, src, count);
+#define SK_OPTS_NS sk_avx
+#include "SkBlend_opts.h"
+
+namespace SkOpts {
+    void Init_avx() { }
 }