build: track config args

Record the ./configure arguments used and make them user-visible.

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
Acked-by: Paul Jakma <paul@jakma.org>
diff --git a/lib/version.h.in b/lib/version.h.in
index 7e9985f..aef1d09 100644
--- a/lib/version.h.in
+++ b/lib/version.h.in
@@ -45,6 +45,8 @@
 
 #define QUAGGA_COPYRIGHT "Copyright 1996-2005 Kunihiro Ishiguro, et al."
 
+#define QUAGGA_CONFIG_ARGS "@CONFIG_ARGS@"
+
 pid_t pid_output (const char *);
 
 #ifndef HAVE_DAEMON