[CI] Add pre-check script to check sphinx doc build. (#4956)

Introduce the check stage to the unittest stage for now
so we don't have to rebuild CI images.
As we make additional CPU images to make use of the sphinx,
consider move it to an earlier stage.

Jenkinsfile

@@ -256,6 +256,7 @@ stage('Unit Test') {
         init_git()
         unpack_lib('gpu', tvm_multilib)
         timeout(time: max_time, unit: 'MINUTES') {
+          sh "${docker_run} ${ci_gpu} ./tests/scripts/task_sphinx_precheck.sh"
           sh "${docker_run} ${ci_gpu} ./tests/scripts/task_python_unittest.sh"
           sh "${docker_run} ${ci_gpu} ./tests/scripts/task_python_integration.sh"
         }

tests/scripts/task_sphinx_precheck.sh

+#!/bin/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.
+
+# Precheck if sphinx docs build can fail.
+set -e
+set -u
+set -o pipefail
+
+cleanup()
+{
+  rm -rf /tmp/$$.*
+}
+trap cleanup 0
+
+# cleanup cache
+rm -rf docs/tutorials
+rm -rf docs/vta/tutorials
+find . -type f -path "*.pyc" | xargs rm -f
+
+echo "PreCheck sphinx doc generation WARNINGS.."
+cd docs
+TVM_TUTORIAL_EXEC_PATTERN=none make html 2>/tmp/$$.log.txt
+
+grep -v -E "__mro__|RemovedInSphinx|UserWarning|FutureWarning" < /tmp/$$.log.txt > /tmp/$$.logclean.txt || true
+echo "---------Sphinx Log----------"
+cat /tmp/$$.logclean.txt
+echo "-----------------------------"
+if grep --quiet -E "WARN" < /tmp/$$.logclean.txt; then
+    echo "WARNINIG found in the log, please fix them."
+    echo "You can reproduce locally by running ./tests/script/task_sphinx_precheck.sh"
+    exit 1
+fi
+echo "No WARNINGS to be fixed."