Build: devel: Replace indent with clang-format.

The indent tool has fallen out of favor with a lot of developers, while
clang-format seems to be growing in popularity. We're not enforcing the
usage of any style tool because they never get everything 100% right,
and I'm not really sure anyone ever actually uses this target - I know I
never have.

However, this at least updates it to be something more modern should
anyone want to use it. To generate this config, I dumped the default
GNU coding style (clang-format -style=gnu -dump-config), removed
anything that wasn't related to regular old C, and then went through
every config option and checked to make sure it was close to our
existing style. I'm sure something incorrect has snuck through.