http://ftp.netbsd.org/pub/pkgsrc/current/pkgsrc/chat/jabberd2/patches/patch-configure
https://github.com/jabberd2/jabberd2/issues/34
--- configure.orig	2015-10-30 03:53:19.000000000 -0500
+++ configure	2015-11-08 22:27:21.000000000 -0600
@@ -11830,7 +11830,7 @@
 # check for optimisation level
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking CFLAGS optimization level" >&5
 $as_echo_n "checking CFLAGS optimization level... " >&6; }
-if echo $CFLAGS | grep '.*-O[3s].*' >/dev/null 2>&1; then
+if echo $CFLAGS | grep '.*-O[3].*' >/dev/null 2>&1; then
     as_fn_error $? "maximum allowed optimization level is -O2" "$LINENO" 5
 fi
 { $as_echo "$as_me:${as_lineno-$LINENO}: result: fine" >&5