file.c: export sprintmode and move it to a separate file

* printmode.c: New file.
* Makefile.am (strace_SOURCES): Add it.
* defs.h (sprintmode): New prototype.
* file.c (sprintmode): Make global and move to printmode.c.
diff --git a/Makefile.am b/Makefile.am
index f7e477a..bae7d43 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -46,6 +46,7 @@
 	or1k_atomic.c	\
 	pathtrace.c	\
 	personality.c	\
+	printmode.c	\
 	process.c	\
 	ptp.c		\
 	quota.c		\