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

[Mark Danial via llvm-commits]

madanial0 wrote:

> Is that lit's internal echo command? What is the bug and why does it only affect AIX?

Yes, for some reason the `-n` doesn't get processed by lit's internal shell and it ends up being echo'd instead of treated like an option 

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