file.c: move chdir parser to a separate file

* chdir.c: New file.
* Makefile.am (strace_SOURCES): Add it.
* file.c (sys_chdir): Move to chdir.c.
diff --git a/Makefile.am b/Makefile.am
index e78e1fe..f068f7e 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -22,6 +22,7 @@
 	block.c		\
 	cacheflush.c	\
 	capability.c	\
+	chdir.c		\
 	chmod.c		\
 	chown.c		\
 	count.c		\