process.c: move exit parser to a separate file

* exit.c: New file.
* Makefile.am (strace_SOURCES): Add it.
* process.c (sys_exit): Move to exit.c.
diff --git a/Makefile.am b/Makefile.am
index 3671ce0..d03d90c 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -32,6 +32,7 @@
 	desc.c		\
 	dirent.c	\
 	execve.c	\
+	exit.c		\
 	fadvise.c	\
 	fallocate.c	\
 	fanotify.c	\