[llvm] Add flags to dump IR to a file before and after LLVM passes (PR #65179)

[Nuri Amari via llvm-commits]

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+config.suffixes = ['', '.ll']
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NuriAmari wrote:

This is because in LIT `%s` expands to the source file path with periods escaped like so: `.../dump-before-after-filenames\\.`, which won't match the output of `find`. 

I also considered running `ls` on each file, but I think the output of filecheck on find is a little easier to read when it fails.

https://github.com/llvm/llvm-project/pull/65179