实现SYS_RMDIR (#566)

* 实现rmdir系统调用，整理do_remove_dir逻辑

kernel/src/syscall/mod.rs

@@ -408,6 +408,12 @@ impl Syscall {
                 }
             }
 
+            #[cfg(target_arch = "x86_64")]
+            SYS_RMDIR => {
+                let pathname = args[0] as *const u8;
+                Self::rmdir(pathname)
+            }
+
             #[cfg(target_arch = "x86_64")]
             SYS_UNLINK => {
                 let pathname = args[0] as *const u8;

kernel/src/syscall/syscall_num.h

@@ -65,6 +65,8 @@
 
 #define SYS_MKDIR 83
 
+#define SYS_RMDIR 84
+
 #define SYS_GETTIMEOFDAY 96
 
 #define SYS_ARCH_PRCTL 158