[llvm] [llvm] don't merge constants with COMDAT (PR #192477)

[Alexis Engelke via llvm-commits]

https://github.com/aengelke commented:

In principle, they could also be merged if the comdat group is the same. I'd rather move the check to makeMergeable below.

Do you have data how this affects, e.g., a stage2 clang build?

https://github.com/llvm/llvm-project/pull/192477