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

[Paul Kirth via llvm-commits]

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@@ -0,0 +1,49 @@
+# C Program to generate all ASCII characters in allchars.txt
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ilovepi wrote:

```suggestion
## C Program to generate all ASCII characters in allchars
```
The file is `allchars`. If you change the extension, please match it.

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