[llvm] [AIX] Fix AIX failures due to switch to internal shell (PR #160566)

[James Henderson via llvm-commits]

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@@ -1,11 +1,13 @@
 ## Show that llvm-strings can handle stdin input properly.
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jh7370 wrote:

Please revert the changes to this test - stdin testing is significant to llvm-strings in particular. If you can't make a quick fix to the test, add an `XFAIL` or similar.

https://github.com/llvm/llvm-project/pull/160566