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

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

core/shared/utils/uncommon/bh_read_file.c

@@ -0,0 +1,53 @@
+#include "bh_read_file.h"
+
+#include <sys/stat.h>
+#include <fcntl.h>
+#include <unistd.h>
+
+char*
+bh_read_file_to_buffer(const char *filename, uint32 *ret_size)
+{
+    char *buffer;
+    int file;
+    uint32 file_size, read_size;
+    struct stat stat_buf;
+
+    if (!filename || !ret_size) {
+        printf("Read file to buffer failed: invalid filename or ret size.\n");
+        return NULL;
+    }
+
+    if ((file = open(filename, O_RDONLY, 0)) == -1) {
+        printf("Read file to buffer failed: open file %s failed.\n",
+               filename);
+        return NULL;
+    }
+
+    if (fstat(file, &stat_buf) != 0) {
+        printf("Read file to buffer failed: fstat file %s failed.\n",
+               filename);
+        close(file);
+        return NULL;
+    }
+
+    file_size = (uint32)stat_buf.st_size;
+
+    if (!(buffer = BH_MALLOC(file_size))) {
+        printf("Read file to buffer failed: alloc memory failed.\n");
+        close(file);
+        return NULL;
+    }
+
+    read_size = (uint32)read(file, buffer, file_size);
+    close(file);
+
+    if (read_size < file_size) {
+        printf("Read file to buffer failed: read file content failed.\n");
+        BH_FREE(buffer);
+        return NULL;
+    }
+
+    *ret_size = file_size;
+    return buffer;
+}
+

core/shared/utils/uncommon/bh_read_file.h

@@ -0,0 +1,23 @@
+/*
+ * Copyright (C) 2019 Intel Corporation.  All rights reserved.
+ * SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+ */
+
+#ifndef _BH_FILE_H
+#define _BH_FILE_H
+
+#include "bh_platform.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+char *
+bh_read_file_to_buffer(const char *filename, uint32 *ret_size);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* end of _BH_FILE_H */
+

core/shared/utils/uncommon/shared_uncommon.cmake

@@ -0,0 +1,11 @@
+# Copyright (C) 2019 Intel Corporation.  All rights reserved.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+set (UNCOMMON_SHARED_DIR ${CMAKE_CURRENT_LIST_DIR})
+
+include_directories(${UNCOMMON_SHARED_DIR})
+
+file (GLOB_RECURSE source_all ${UNCOMMON_SHARED_DIR}/*.c)
+
+set (UNCOMMON_SHARED_SOURCE ${source_all})
+