file.c: move chmod, fchmod, and fchmodat parsers to a separate file

* chmod.c: New file.
* Makefile.am (strace_SOURCES): Add it.
* file.c (sys_chmod, sys_fchmodat, sys_fchmod): Move to chmod.c.
diff --git a/Makefile.am b/Makefile.am
index 5452d00..664475e 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -22,6 +22,7 @@
 	block.c		\
 	cacheflush.c	\
 	capability.c	\
+	chmod.c		\
 	count.c		\
 	desc.c		\
 	dirent.c	\