Parallelize clang-format with multiple files.

[ActuallyaDeviloper]

Currently it seems clang-format will process each file one after another if multiple are specified. This can be tramendously slow when formatting an entire project.

Clang-format should be able to process all specified files in parallel.

[llvmbot]

@llvm/issue-subscribers-clang-format

Author: None (ActuallyaDeviloper)

Currently it seems clang-format will process each file one after another if multiple are specified. This can be tramendously slow when formatting an entire project.

Clang-format should be able to process all specified files in parallel.

[EugeneZelenko]

Clang-Tidy implement multi-processing via run-clang-tidy.py script.

[vbvictor]

When I run clang-format over all clang-tools-extra/clang-tidy directory, I created such script:
https://gist.github.com/vbvictor/5414a14a90f26ef48cd297af42b7470c.
99% of the script itself made by AI and the design is heavily influenced by run-clang-tidy.py (which is probably bad).

I didn't test any flags except for this command: ./run-clang-format.py -i clang-tools-extra/clang-tidy/.
Feel free to take script or try to push it to LLVM.