Break out SSE functions into new media_sse target.

media/base/vector_math_testing.h

Index: media/base/vector_math_testing.h
diff --git a/media/base/vector_math_testing.h b/media/base/vector_math_testing.h
index d364b74e65d45848997de2f443136edd168d163b..503ca6a396adbc372484920c7fb069a74def657b 100644
--- a/media/base/vector_math_testing.h
+++ b/media/base/vector_math_testing.h
@@ -5,6 +5,7 @@
 #ifndef MEDIA_BASE_VECTOR_MATH_TESTING_H_
 #define MEDIA_BASE_VECTOR_MATH_TESTING_H_
 
+#include "build/build_config.h"
 #include "media/base/media_export.h"
 
 namespace media {
@@ -13,8 +14,11 @@ namespace vector_math {
 // Optimized versions of FMAC() function exposed for testing.  See vector_math.h
 // for details.
 MEDIA_EXPORT void FMAC_C(const float src[], float scale, int len, float dest[]);
+
+#if defined(ARCH_CPU_X86_FAMILY)
 MEDIA_EXPORT void FMAC_SSE(const float src[], float scale, int len,
                            float dest[]);
+#endif
 
 }  // namespace vector_math
 }  // namespace media