Detect if make(1) is GNU make, to avoid confusing debian kFreeBSD.

configure

@@ -74,8 +74,18 @@ SRCS='
 	udp.c
 '
 
-if [ -f /usr/share/mk/bsd.prog.mk ] ; then
+if make -v 2>&1 | grep -q GNU ; then
+	echo "make(1) is GNU make."
+	BSD=false
+elif [ -f /usr/share/mk/bsd.prog.mk ] ; then
 	echo "Found bsd.prog.mk, will use it."
+	BSD=true
+else
+	echo "Defaulting to plain makefile"
+	BSD=false
+fi
+
+if $BSD ; then
 	(
 	echo '# BSD-style Makefile generated by configure'
 	echo 'PROG	=	ntimed-client'