[llvm] [llvm-lit][test] Precommit tests for lit's built-in cat command (PR #101530)

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+# C Program to generate all ASCII characters in allchars.txt
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connieyzhu wrote:

I believe the special characters themselves make the file binary. Even when the files used to have the .txt extension, it would still be marked as a binary file. I tried adding some leading strings but it didn't change anything.

https://github.com/llvm/llvm-project/pull/101530