Don't support fd sync flags

It's not yet clear whether these flags should be added to the standard
so disallow use of them for the time being. See
WebAssembly/wasi-filesystem#98 for more
details. These changes are also necessary to ensure the rust WASI tests
pass since they assert that path_open returns ENOTSUP when passing
O_DSYNC/O_RSYNC/O_SYNC.

core/iwasm/libraries/libc-wasi/sandboxed-system-primitives/src/posix.c

@@ -1800,16 +1800,16 @@ wasmtime_ssp_path_open(
         needed_base |= __WASI_RIGHT_PATH_FILESTAT_SET_SIZE;
     }
 
-    // Convert file descriptor flags.
-    if ((fs_flags & __WASI_FDFLAG_DSYNC) != 0) {
-        needed_inheriting |= __WASI_RIGHT_FD_DATASYNC;
-    }
-    if ((fs_flags & __WASI_FDFLAG_RSYNC) != 0) {
-        needed_inheriting |= __WASI_RIGHT_FD_SYNC;
-    }
-    if ((fs_flags & __WASI_FDFLAG_SYNC) != 0) {
-        needed_inheriting |= __WASI_RIGHT_FD_SYNC;
+    // It's not clear whether we want to support these flags in the standard
+    // yet: https://github.com/WebAssembly/wasi-filesystem/issues/98 so disable
+    // them in the meanwhile.
+    if (((fs_flags & __WASI_FDFLAG_DSYNC) != 0)
+        || ((fs_flags & __WASI_FDFLAG_RSYNC) != 0)
+        || ((fs_flags & __WASI_FDFLAG_SYNC) != 0)) {
+        return __WASI_ENOTSUP;
     }
+
+    // Convert file descriptor flags.
     if (write
         && !((fs_flags & __WASI_FDFLAG_APPEND) || (__WASI_O_TRUNC & oflags)))
         needed_inheriting |= __WASI_RIGHT_FD_SEEK;