contrib/jenkins.sh: Enable Werror in C(PP)FLAGS

Change-Id: Id4724fe07f6641e82c3bd9cde2d8d759aa492288
diff --git a/contrib/jenkins.sh b/contrib/jenkins.sh
index 6a718a8..4437541 100755
--- a/contrib/jenkins.sh
+++ b/contrib/jenkins.sh
@@ -35,7 +35,7 @@
 
 cd "$base"
 autoreconf --install --force
-./configure $GTP
+./configure CFLAGS="-Werror" CPPFLAGS="-Werror" $GTP
 $MAKE $PARALLEL_MAKE
 $MAKE distcheck