linux-sgx: Allow to open files with arbitrary paths in the sandbox using IPFS (#1685)

A limitation of the current implementation of SGX IPFS in WAMR is that
it prevents to open files which are not in the current directory.
This restriction is lifted and can now open files in paths, similarly to the
WASI openat call, which takes into account the sandbox of the file system.

samples/file/wasm-app/main.c

@@ -12,7 +12,8 @@
 #include <sys/stat.h>
 #include <unistd.h>
 
-#define PATH_TEST_FILE "test.txt"
+#define PATH_TEST_FOLDER "./test"
+#define PATH_TEST_FILE (PATH_TEST_FOLDER "/test.txt")
 #define FILE_TEXT "Hello, world!"
 #define WORLD_OFFSET 7
 #define NAME_REPLACMENT "James"
@@ -28,6 +29,10 @@ main(int argc, char **argv)
     int ret;
     long long stat_size;
 
+    // Test: Create a folder to store the file, if it does not exist yet
+    ret = mkdir(PATH_TEST_FOLDER, 777);
+    assert(ret == 0 || (ret == -1 && errno == EEXIST));
+
     // Test: File opening (fopen)
     printf("Opening a file..\n");
     file = fopen(PATH_TEST_FILE, "w+");