Fix #4251 --file-filter option removed for cppcheck handler

[juanmitaboada]

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--file-filter option has been removed because using it prevents cppcheck from processing the file if it is in a different path

[w0rp]

I'll have to have a think about this before I merge it. It's probably right.

[w0rp]

Projects often have a structure such as src/*.cpp for all source files. Running cppcheck on the entire directly could be slow without a file filter, which I belive is the reason the filter is in place. I think the solution the problem here is the following:

1. Edit the linter so it runs in a specific cwd.
2. Keep --filte-filter and so it to a path relative to the cwd that was selected for the linter.

ALE has functions in ale#path that can be used for this purpose. You can do that and update the tests to test for it.

Thanks for looking into this!

[stale[bot]]

This pull request has been automatically marked as stale because it has not been updated recently. Make sure to write tests and document your changes. See :help ale-dev for information on writing tests. If your pull request is good to merge, bother w0rp or another maintainer again, and get them to merge it.