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

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

core/shared/utils/bh_assert.h

@@ -0,0 +1,29 @@
+/*
+ * Copyright (C) 2019 Intel Corporation.  All rights reserved.
+ * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+ */
+
+#ifndef _BH_ASSERT_H
+#define _BH_ASSERT_H
+
+#include "bh_platform.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#if BH_DEBUG != 0
+void bh_assert_internal(int v, const char *file_name, int line_number,
+                        const char *expr_string);
+#define bh_assert(expr) bh_assert_internal((int)(uintptr_t)(expr), \
+                                            __FILE__, __LINE__, #expr)
+#else
+#define bh_assert(expr) (void)0
+#endif /* end of BH_DEBUG */
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* end of _BH_ASSERT_H */
+