Create script for updating submodules

We have to update LLVM, MLIR, and TF modules all the time and this should make it slightly less painful. It's got some checks in there and also doesn't do the actual push, so should also be reasonably safe.

Closes #183

COPYBARA_INTEGRATE_REVIEW=https://github.com/google/iree/pull/183 from google:submodule 21cc64684242497fa5ee5878678d1b5af86b6244
PiperOrigin-RevId: 284873268

build_tools/scripts/update_submodules.sh

diff --git a/build_tools/scripts/update_submodules.sh b/build_tools/scripts/update_submodules.sh
new file mode 100755
index 0000000..ca3a0e5
--- /dev/null
+++ b/build_tools/scripts/update_submodules.sh
@@ -0,0 +1,64 @@
+#!/bin/bash
+
+# Copyright 2019 Google LLC
+#
+# Licensed 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
+#
+#      https://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.
+
+# Updates the LLVM, MLIR, and TF submodules and pushes a commit to master.
+
+# This is scripted because we have to do this all the time as we get out of
+# sync between GitHub and upstream. It's not a more sophisticated fix
+# because we're waiting until MLIR moves to LLVM to do something more
+# robust here.
+
+set -e
+
+current_branch="$(git branch --show-current)"
+
+if [ "$current_branch" != "master" ]; then
+  echo "Current branch (${current_branch}) is not master. Aborting."
+  exit 1
+fi
+
+git_status="$(git status -s)"
+
+if [ -n "$git_status" ]; then
+  echo "Modified/untracked files in working directory. Aborting."
+  exit 1
+fi
+
+echo "Pulling latest from remote"
+git pull
+
+git_status="$(git status -s)"
+
+if [ -n "$git_status" ]; then
+  echo "Modified/untracked files in working directory after pull. Aborting."
+  exit 1
+fi
+
+echo "Updating LLVM, MLIR, TF submodules to latest"
+
+git submodule update --remote third_party/llvm-project third_party/mlir third_party/tensorflow
+
+MSG="Update LLVM, MLIR, TF submodules to latest
+
+\$ ./build_tools/scripts/update_submodules.sh
+"
+
+git commit -am "$MSG"
+
+echo -e "\n\n\nCreated commit. Please confirm message and diffs before pushing"
+
+git log -n 1
+git diff origin/master