Move sync code to include/, switch from using platform define to a proxy header in core/

src/ports/SkBarriers_arm.h

-/*
- * Copyright 2014 Google Inc.
- *
- * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file.
- */
-
-#ifndef SkBarriers_arm_DEFINED
-#define SkBarriers_arm_DEFINED
-
-static inline void sk_compiler_barrier() { asm volatile("" : : : "memory"); }
-
-template <typename T>
-T sk_acquire_load(T* ptr) {
-    T val = *ptr;
-    __sync_synchronize();  // Issue a full barrier, which is an overkill acquire barrier.
-    return val;
-}
-
-template <typename T>
-T sk_consume_load(T* ptr) {
-    T val = *ptr;
-    // Unlike acquire, consume loads (data-dependent loads) are guaranteed not to reorder on ARM.
-    // No memory barrier is needed, so we just use a compiler barrier.
-    // C.f. http://preshing.com/20140709/the-purpose-of-memory_order_consume-in-cpp11/
-    sk_compiler_barrier();
-    return val;
-}
-
-template <typename T>
-void sk_release_store(T* ptr, T val) {
-    __sync_synchronize();  // Issue a full barrier, which is an overkill release barrier.
-    *ptr = val;
-}
-
-#endif//SkBarriers_x86_DEFINED