cmake: add script to update sanitizers cmake files

problem: git subtree is arcane

solution: add a script to pull changes into the subtree

Author: trws

cmake/update-sanitizers-cmake.sh

@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+# first version pulled from commit 3f0542e on April 19
+# add command: git subtree add --prefix=cmake/sanitizers-cmake --squash https://github.com/arsenm/sanitizers-cmake master
+#
+# To rebase across an update, use `git rebase --rebase-merges --strategy subtree
+# if the rebase stops and says "refusing to merge unrelated histories" then use
+# the add command above or pull or similar to re-create the merge commit
+git subtree pull --prefix cmake/sanitizers-cmake https://github.com/arsenm/sanitizers-cmake master --squash