This relieves me of the cognitive burden of having to think about
trivial formatting details (especially when reviewing code from others,
but also for myself).  In most cases the reformatted code is equivalent
or superior in terms of my preferred style to what I wrote myself.

* .clang-format: New file.
* .pre-commit-config.yaml: Add clang-format hook.
* include/*, lib/*, libdb/*, src/*: Reformat using clang-format.