Refactor to put SkXfermode_opts inside SK_OPTS_NS.

src/core/SkNx.h

Index: src/core/SkNx.h
diff --git a/src/core/SkNx.h b/src/core/SkNx.h
index 84f9b693537bdae6a56d4cb09757da8942400353..728e450ebbb9dcec7290c731b3d8781dae9e49b5 100644
--- a/src/core/SkNx.h
+++ b/src/core/SkNx.h
@@ -17,13 +17,6 @@
 #include <math.h>
 #define REQUIRE(x) static_assert(x, #x)
 
-// This file may be included multiple times by .cpp files with different flags, leading
-// to different definitions.  Usually that doesn't matter because it's all inlined, but
-// in Debug modes the compilers may not inline everything.  So wrap everything in an
-// anonymous namespace to give each includer their own silo of this code (or the linker
-// will probably pick one randomly for us, which is rarely correct).
-namespace {
-
 // The default implementations just fall back on a pair of size N/2.
 
 template <int N, typename T>
@@ -252,8 +245,6 @@ protected:
     T fVal;
 };
 
-}  // namespace
-
 // Include platform specific specializations if available.
 #ifndef SKNX_NO_SIMD
     #if SK_CPU_SSE_LEVEL >= SK_CPU_SSE_LEVEL_SSE2