Accords gradle build fails due to ephemeral issues with rat and checkstyle

patch by David Capwell; reviewed by Michael Semb Wever for CASSANDRA-20590

.build/build-accord.xml

@@ -27,10 +27,16 @@
         <arg value="publishToMavenLocal" />
         <arg value="-x" />
         <arg value="test" />
-        <!-- since so much development is done from this hook, by adding checkstyle and rat will avoid issues earlier -->
+        <!-- Disable rat/checkstyle as C*'s logic will include the accord source -->
+        <arg value="-x" />
         <arg value="rat" />
+        <arg value="-x" />
         <arg value="checkstyleMain" />
+        <arg value="-x" />
         <arg value="checkstyleTest" />
+        <arg value="-x" />
+        <arg value="javadoc" />
+        <arg value="--stacktrace" />
         <arg value="-Paccord_group=org.apache.cassandra" />
         <arg value="-Paccord_artifactId=cassandra-accord" />
         <arg value="-Paccord_version=${version}" />

.build/build-rat.xml

@@ -30,6 +30,7 @@
         <exec executable="git" failifexecutionfails="false" failonerror="false" resultproperty="git.success" output="${build.dir}/.ratinclude">
             <arg line="ls-tree -r HEAD --name-only"/>
         </exec>
+        <exec executable="${build.helpers.dir}/rat-include-accord.sh" failifexecutionfails="false" failonerror="false" resultproperty="git.success"  output="${build.dir}/.ratinclude" append="true" />
         <condition property="rat.skip" value="true">
             <not>
                 <equals arg1="${git.success}" arg2="0"/>

.build/rat-include-accord.sh

@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+#set -o xtrace
+set -o errexit
+set -o pipefail
+set -o nounset
+
+home="$(cd "$(dirname "$0")"/.. > /dev/null; pwd)"
+
+git --git-dir="$home"/modules/accord/.git ls-tree -r HEAD --name-only | sed 's;^;modules/accord/;'