Add script from stack overflow for rewriting subtree commits
We need to rewrite subtree commits in order to put the Change ID in the
footer of the subtree commits. So script it! This script is from
stack overflow.
Change-Id: Icc1fae32ca2f5bc60fc969fedac41caf8c14005a
diff --git a/third_party/rewrite_subtree.sh b/third_party/rewrite_subtree.sh
new file mode 100755
index 0000000..a3e5372
--- /dev/null
+++ b/third_party/rewrite_subtree.sh
@@ -0,0 +1,23 @@
+#!/bin/bash
+#
+# Coppied from:
+# https://stackoverflow.com/questions/40297499/pushing-squashed-subtree-change-to-gerrit
+#
+# This command re-writes the history after doing a git subtree {pull|add}
+# to add Gerrit Change-Id lines to the squash commit message.
+#
+# It assumes that HEAD is the merge commit merging the subtree into HEAD.
+# The original HEAD commit will be backed up under refs/original, which
+# is helpful if something goes wrong.
+
+set -e
+set -o pipefail
+
+GIT_DIR=$(readlink -f "$(git rev-parse --git-dir)")
+TMP_MSG="${GIT_DIR}/COMMIT_MSG_REWRITE"
+
+git filter-branch --msg-filter \
+ "cat > ${TMP_MSG} && \"${GIT_DIR}/hooks/commit-msg\" ${TMP_MSG} && \
+ cat \"${TMP_MSG}\"" HEAD...HEAD~1
+
+rm -rf "${TMP_MSG}"