[clang] [CIR] Fix use-after-free in conditional-operator codegen (PR #210148)

[Andy Kaylor via cfe-commits]

andykaylor wrote:

@bcardosolopes The same fix was proposed in https://github.com/llvm/llvm-project/pull/208850 by @kumarak 

I didn't think it looked robust and suggested an alternate implementation, which I have approved but hadn't yet merged. Let me know what you think of the alternate fix.

https://github.com/llvm/llvm-project/pull/210148