CI: error on printf format problems, simplify local reproduction

1. Remove --enable-ubsan configure option

Setting CFLAGS and LDFLAGS on the command line works fine.

2. Move default CI configure flags to autogen.sh

The yaml file just calls autogen.sh --ci and autogen.sh adds all the CI parameters when it calls configure.

This makes it easier for a developer to configure with the exact set of flags that are used in CI without having to remember them all.

3. Enable the Undefined Behavior Sanitizer in CI

I wonder what the performance impact will be. It added 5-6% to the pipeline time. May revisit later.

4. Treat printf format warnings as errors in CI