[clang] [llvm] [clang] Add more test coverage for "zero-call-used-regs" (PR #201834)

[Lucas Chollet via cfe-commits]

LucasChollet wrote:

Thanks for the review! (Also, I don't have write permissions here, so I will need help to merge the PR.)

https://github.com/llvm/llvm-project/pull/201834