Try again to put SkXfermode_opts in SK_OPTS_NS

src/opts/SkOpts_ssse3.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 "SkOpts.h"
 #define SK_OPTS_NS sk_ssse3
 #include "SkBlitMask_opts.h"
 #include "SkColorCubeFilter_opts.h"
 #include "SkXfermode_opts.h"
 
 namespace SkOpts {
     void Init_ssse3() {
-        create_xfermode = SkCreate4pxXfermode;
+        create_xfermode = sk_ssse3::create_xfermode;
         blit_mask_d32_a8 = sk_ssse3::blit_mask_d32_a8;
         color_cube_filter_span = sk_ssse3::color_cube_filter_span;
     }
 }