[clang] [clang][test] Rewrote test to work with lit internal shell syntax (PR #105902)

[Paul Kirth via cfe-commits]

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+import argparse
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ilovepi wrote:

> Test files generally do not have license headers. 

Ah, right. I was thinking of them differently, since they're not par to of the test per se, but now that you spell it out, that makes sense. Thanks.

https://github.com/llvm/llvm-project/pull/105902