Bug fixes for fcntl and o_cloexec

Add fcntl to schemes
Fix debug: hang

src/scheme/memory.rs

@@ -23,7 +23,11 @@ impl Scheme for MemoryScheme {
         Ok(0)
     }
 
-    fn fpath(&self, id: usize, buf: &mut [u8]) -> Result<usize> {
+    fn fcntl(&self, _id: usize, _cmd: usize, _arg: usize) -> Result<usize> {
+        Ok(0)
+    }
+
+    fn fpath(&self, _id: usize, buf: &mut [u8]) -> Result<usize> {
         let mut i = 0;
         let scheme_path = b"memory:";
         while i < buf.len() && i < scheme_path.len() {