clang-format: ignore generated files

clang-format: ignore generated files

Two auto-generated files cause clang-format < v17 to hang when
they are being formatted. I have not looked into the root-cause,
but formatting them is useless anyhow.

Adding them to .clang-format-ignore works around the problem for the
moment.

Since clang-format 14 does not support ignore files, their support is
crudely emulated here using grep to filter out find's results.

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: I1cd10349ef1a66b1d595105b0ec1a4beef9dcc9a