contrib: Enable -Werror by default

Change-Id: I2a88cdcbf76ea28a30e82836030f894c2152d5ed
diff --git a/contrib/jenkins.sh b/contrib/jenkins.sh
index 7a388c2..79d101e 100755
--- a/contrib/jenkins.sh
+++ b/contrib/jenkins.sh
@@ -4,6 +4,6 @@
 
 autoreconf --install --force
 ./configure
-$MAKE
+$MAKE CFLAGS="-Werror" CPPFLAGS="-Werror"
 # currently broken $MAKE $PARALLEL_MAKE
 # currently broken $MAKE distcheck