New contributors can just indicate that they are working on the issue
without requesting assignment.

That shouldd reduce the burden of assigned issues that are not actually
being worked on, and new contributors waiting for a maintainer to
asssign them the issue.

---------

Co-authored-by: Danny Mösch <danny.moesch@icloud.com>

This script is not working any more in the GitHub actions jobs and I
can't reproduce this locally, so I've added some debug output to try to
help find the problem.

In clang-format, OpenCL .cl file uses default C++ formatting. There are
many pull-requests in libclc project that change OpenCL files. It is
beneficial to enable clang-format for them in CI.

Only check for diffs containing "undef" in .ll files, this prevents
comments like `// We should not have undef values...` triggering the
undef checker bot.

If the list of filtered files was empty the check would process every
file in the diff.

It's common to use the /cherry-pick command on a PR to create a backport
request. However, this creates a lot of clutter in the LLVM Release
Status project, because we end up with two items in the project, one for
the original PR and one for the new PR.

This change will set the status of the original PR to Done once the new
PR (for the release branch) is created. This will save release managers
a lot of work of having to manually updated the status for PRs that
contain backport requests.

* Greet the user and ask them to read the developer policy.
* Post their contribution stats on the issue.