[llvm] Fix crash from [CGData] Global Merge Functions (#112671) (PR #116241)

[Mikael Holmén via llvm-commits]

mikaelholmen wrote:

This fixes the crash I reported in https://github.com/llvm/llvm-project/pull/112671#issuecomment-2475770532
I have no idea if this is the propoer fix for the problem though. I think it's better if someone who reviwed https://github.com/llvm/llvm-project/pull/112671 looks at this too.

I think it would be good to add a testcase though. There is a reproducer in https://github.com/llvm/llvm-project/pull/112671#issuecomment-2475770532 so it's easy to make a testcase out of that.

https://github.com/llvm/llvm-project/pull/116241