re-org platform APIs, simplify porting process (#201)

Co-authored-by: Xu Jun <jun1.xu@intel.com>

core/shared/utils/bh_platform.h

@@ -0,0 +1,40 @@
+/*
+ * Copyright (C) 2019 Intel Corporation.  All rights reserved.
+ * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+ */
+
+#ifndef _BH_PLATFORM_H
+#define _BH_PLATFORM_H
+
+#include "../platform/include/platform_common.h"
+#include "../platform/include/platform_api_vmcore.h"
+#include "../platform/include/platform_api_extension.h"
+#include "bh_assert.h"
+#include "bh_common.h"
+#include "bh_hashmap.h"
+#include "bh_list.h"
+#include "bh_log.h"
+#include "bh_queue.h"
+#include "runtime_timer.h"
+
+
+
+/**
+ * WA_MALLOC/WA_FREE need to be redefined for both
+ * runtime native and WASM app respectively.
+ *
+ * Some source files are shared for building native and WASM,
+ * and this the mem allocator API for these files.
+ *
+ * Here we define it for the native world
+ */
+#ifndef WA_MALLOC
+#define WA_MALLOC wasm_runtime_malloc
+#endif
+
+#ifndef WA_FREE
+#define WA_FREE wasm_runtime_free
+#endif
+
+#endif /* #ifndef _BH_PLATFORM_H */
+