autogen.sh: use exec instead of waiting for configure to finish

Syncs the invocation of configure with the one from the server.
Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>

autogen.sh

@@ -10,5 +10,5 @@ autoreconf -v --install || exit 1
 cd $ORIGDIR || exit $?
 
 if test -z "$NOCONFIGURE"; then
-    $srcdir/configure "$@"
+    exec $srcdir/configure "$@"
 fi