Clean up dead xfermode opts code.

src/opts/SkXfermode_opts_arm.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 "SkXfermode.h"
 #include "SkXfermode_proccoeff.h"
 #include "SkUtilsArm.h"
 
-extern SkProcCoeffXfermode* SkPlatformXfermodeFactory_impl_neon(const ProcCoeff& rec,
-                                                                SkXfermode::Mode mode);
+// If we find we do have NEON, we'll call this method from SkXfermodes_opts_arm_neon.cpp.
+SkProcCoeffXfermode* SkPlatformXfermodeFactory_impl_neon(const ProcCoeff& rec,
+                                                         SkXfermode::Mode mode);
 
-extern SkXfermodeProc SkPlatformXfermodeProcFactory_impl_neon(SkXfermode::Mode mode);
-
-SkProcCoeffXfermode* SkPlatformXfermodeFactory_impl(const ProcCoeff& rec,
-                                                    SkXfermode::Mode mode) {
+// If we don't have NEON, we'll call this method and return NULL.
+SkProcCoeffXfermode* SkPlatformXfermodeFactory_impl(const ProcCoeff& rec, SkXfermode::Mode mode);
+SkProcCoeffXfermode* SkPlatformXfermodeFactory_impl(const ProcCoeff& rec, SkXfermode::Mode mode) {
     return NULL;
 }
 
-SkXfermodeProc SkPlatformXfermodeProcFactory_impl(SkXfermode::Mode mode) {
-    return NULL;
-}
-
-SkProcCoeffXfermode* SkPlatformXfermodeFactory(const ProcCoeff& rec,
-                                               SkXfermode::Mode mode) {
+SkProcCoeffXfermode* SkPlatformXfermodeFactory(const ProcCoeff& rec, SkXfermode::Mode mode);
+SkProcCoeffXfermode* SkPlatformXfermodeFactory(const ProcCoeff& rec, SkXfermode::Mode mode) {
     return SK_ARM_NEON_WRAP(SkPlatformXfermodeFactory_impl)(rec, mode);
 }
 
-SkXfermodeProc SkPlatformXfermodeProcFactory(SkXfermode::Mode mode) {
-    return SK_ARM_NEON_WRAP(SkPlatformXfermodeProcFactory_impl)(mode);
-}
+SkXfermodeProc SkPlatformXfermodeProcFactory(SkXfermode::Mode mode);
+SkXfermodeProc SkPlatformXfermodeProcFactory(SkXfermode::Mode mode) { return NULL; }