Don't instruct user to run make when autogen.sh failed

Currently the autogen script will always tell user to run make even
when the configure script failed, this patch changes the behavior to
only show this message when the configure script terminates without
error.

autogen.sh

@@ -76,6 +76,11 @@ fi
 
 if test -z "$NOCONFIGURE"; then
     $srcdir/configure $EXTRA_ARGS "$@"
-    echo
-    echo "Now type 'make' to compile libxml2."
+    if test "$?" -ne 0; then
+        echo
+        echo "Configure script failed, check config.log for more info."
+    else
+        echo
+        echo "Now type 'make' to compile libxml2."
+    fi
 fi