[llvm] [llvm-lit][test] Precommit tests for curly braces in lit internal shell (PR #102976)

[James Henderson via llvm-commits]

jh7370 wrote:

I'm not opposed to this PR being developed, but I don't want it and the follow-on PR landed without the RFC discussion I've requested in the source issue: as noted there, I'm not convinced this functionality is needed in lit (not going to elaborate further here, to avoid splitting the discussion).

https://github.com/llvm/llvm-project/pull/102976