Move dirent related parsers to a separate file

* dirent.c: New file.
* Makefile.am (strace_SOURCES): Add it.
* file.c (print_old_dirent, sys_readdir, sys_getdents, sys_getdents64):
Move to dirent.c.
diff --git a/Makefile.am b/Makefile.am
index a30ac1c..7dfdf2c 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -22,6 +22,7 @@
 	block.c		\
 	count.c		\
 	desc.c		\
+	dirent.c	\
 	fanotify.c	\
 	file.c		\
 	inotify.c	\