Make clang-format run on each file independently using add_custom_format (instead using a shell script in utils/). The targets polly-{update|check}-format depend on these.
The primary motivation is to make them work on Windows, but also improves them generally:
- Each file update/check can run in parallel (Although they do not take long to run anyway)
- Implicit dependency on clang-format, so it recompiles if necessary
- polly-check-format shows the formatting difference if failing