lint: Add LogPrint(f) termination linter

Ensures that all LogPrint() and LogPrintf() calls are properly
terminated to avoid conjoined lines in the debug.log file.

test/lint/lint-logs.sh

@@ -0,0 +1,28 @@
+#!/usr/bin/env bash
+#
+# Copyright (c) 2018-2019 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 that all logs are terminated with '\n'
+#
+# Some logs are continued over multiple lines. They should be explicitly
+# commented with \* Continued *\
+#
+# There are some instances of LogPrintf() in comments. Those can be
+# ignored
+
+export LC_ALL=C
+UNTERMINATED_LOGS=$(git grep --extended-regexp "LogPrintf?\(" -- "*.cpp" | \
+    grep -v '\\n"' | \
+    grep -v '\.\.\.' | \
+    grep -v "/\* Continued \*/" | \
+    grep -v "LogPrint()" | \
+    grep -v "LogPrintf()")
+if [[ ${UNTERMINATED_LOGS} != "" ]]; then
+    # shellcheck disable=SC2028
+    echo "All calls to LogPrintf() and LogPrint() should be terminated with \\n"
+    echo
+    echo "${UNTERMINATED_LOGS}"
+    exit 1
+fi