test: Add lint to prevent SIGNAL/SLOT connect style

test/lint/lint-qt.sh

@@ -0,0 +1,20 @@
+#!/usr/bin/env bash
+#
+# Copyright (c) 2018 The Bitcoin Core developers
+# Distributed under the MIT software license, see the accompanying
+# file COPYING or http://www.opensource.org/licenses/mit-license.php.
+#
+# Check for SIGNAL/SLOT connect style, removed since Qt4 support drop.
+
+export LC_ALL=C
+
+EXIT_CODE=0
+
+OUTPUT=$(git grep -E '(SIGNAL|, ?SLOT)\(' -- src/qt)
+if [[ ${OUTPUT} != "" ]]; then
+    echo "Use Qt5 connect style in:"
+    echo "$OUTPUT"
+    EXIT_CODE=1
+fi
+
+exit ${EXIT_CODE}