Fix compiler warnings about unused parameters:

mysys/my_sync.c: In function 'my_sync_dir':
mysys/my_sync.c:103:29: error: unused parameter 'dir_name'
mysys/my_sync.c:103:43: error: unused parameter 'my_flags'
mysys/my_sync.c: In function 'my_sync_dir_by_file':
mysys/my_sync.c:144:37: error: unused parameter 'file_name'
mysys/my_sync.c:144:52: error: unused parameter 'my_flags'

mysys/my_sync.c

@@ -100,9 +100,9 @@ static const char cur_dir_name[]= {FN_CURLIB, 0};
   RETURN
     0 if ok, !=0 if error
 */
+#ifdef NEED_EXPLICIT_SYNC_DIR
 int my_sync_dir(const char *dir_name, myf my_flags)
 {
-#ifdef NEED_EXPLICIT_SYNC_DIR
   File dir_fd;
   int res= 0;
   const char *correct_dir_name;
@@ -124,10 +124,14 @@ int my_sync_dir(const char *dir_name, myf my_flags)
   else
     res= 1;
   DBUG_RETURN(res);
-#else
+}
+#else /* NEED_EXPLICIT_SYNC_DIR */
+int my_sync_dir(const char *dir_name __attribute__((unused)),
+		myf my_flags __attribute__((unused)))
+{
   return 0;
-#endif
 }
+#endif /* NEED_EXPLICIT_SYNC_DIR */
 
 
 /*
@@ -141,15 +145,17 @@ int my_sync_dir(const char *dir_name, myf my_flags)
   RETURN
     0 if ok, !=0 if error
 */
+#ifdef NEED_EXPLICIT_SYNC_DIR
 int my_sync_dir_by_file(const char *file_name, myf my_flags)
 {
-#ifdef NEED_EXPLICIT_SYNC_DIR
   char dir_name[FN_REFLEN];
   size_t dir_name_length;
   dirname_part(dir_name, file_name, &dir_name_length);
   return my_sync_dir(dir_name, my_flags);
-#else
+#else /* NEED_EXPLICIT_SYNC_DIR */
+int my_sync_dir_by_file(const char *file_name __attribute__((unused)),
+			myf my_flags __attribute__((unused)))
+{
   return 0;
-#endif
 }
-
+#endif /* NEED_EXPLICIT_SYNC_DIR */