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

src/ports/SkBarriers_x86.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_x86_DEFINED
-#define SkBarriers_x86_DEFINED
-
-#ifdef SK_BUILD_FOR_WIN
-#  include <intrin.h>
-static inline void sk_compiler_barrier() { _ReadWriteBarrier(); }
-#else
-static inline void sk_compiler_barrier() { asm volatile("" : : : "memory"); }
-#endif
-
-template <typename T>
-T sk_acquire_load(T* ptr) {
-    T val = *ptr;
-    // On x86, all loads are acquire loads, so we only need a compiler barrier.
-    sk_compiler_barrier();
-    return val;
-}
-
-template <typename T>
-T sk_consume_load(T* ptr) {
-    // On x86, consume is the same as acquire, i.e. a normal load.
-    return sk_acquire_load(ptr);
-}
-
-template <typename T>
-void sk_release_store(T* ptr, T val) {
-    // On x86, all stores are release stores, so we only need a compiler barrier.
-    sk_compiler_barrier();
-    *ptr = val;
-}
-
-#endif//SkBarriers_x86_DEFINED