[llvm] [lit] Fix some issues from --per-test-coverage (PR #65242)

[Joel E. Denny via llvm-commits]

jdenny-ornl wrote:

> > (By the way, I have noticed that many python files were formatted with >80 columns, probably the black default of 88. That doesn't fit in the 80-column editor/terminal windows I use for most of LLVM. Is there any good reason not to follow [the LLVM coding standard for source code width](https://llvm.org/docs/CodingStandards.html#source-code-width) in python files? I see no exception there for python, or did I misunderstand something? Black just needs a `-l80` command-line option.)
> 
> This was discussed when we wrote the coding style for python and then we thought it was just better to use black's default to avoid having people need to run black with arguments

OK, but the LLVM coding standard appears to contradict that approach, as far as I can tell:

1. "Write your code to fit within 80 columns."  (From <https://llvm.org/docs/CodingStandards.html#source-code-width>.)
2. "The Python code within the LLVM repository should adhere to the formatting guidelines outlined in [PEP-8](https://peps.python.org/pep-0008/)."  (From <https://llvm.org/docs/CodingStandards.html#python-version-and-source-code-formatting>).
3. "Limit all lines to a maximum of 79 characters." (From <https://peps.python.org/pep-0008/#maximum-line-length>.)

The [LLVM coding standard's advice on using black](https://llvm.org/docs/CodingStandards.html#python-version-and-source-code-formatting) is:

> For consistency and to limit churn, code should be automatically formatted with the [black](https://github.com/psf/black) utility. Black allows changing the formatting rules based on major version. In order to avoid unnecessary churn in the formatting rules we currently use black version 23.x in LLVM.

Combining all the above, I'm led to believe I should be passing options to black, but it's unclear which ones.

I'm sorry I didn't participate in the original discussion.  If it's too late to change things, can we clarify the LLVM coding standard?

> (since it won't read a config file).

See <https://black.readthedocs.io/en/stable/usage_and_configuration/the_basics.html#configuration-via-a-file>.

For example, in `llvm/utils/lit/pyproject.toml `, I appended the following:

```
[tool.black]
line-length = 80
```

And it worked for me.

https://github.com/llvm/llvm-project/pull/65242