[llvm] [llvm/IR] Fix module build issue following e57308b063bb (NFC) (PR #94580)

[Med Ismail Bennani via llvm-commits]

medismailben wrote:

@nikic I went with the lowest common denominator (which was `Constant.h`) since I thought I'd need to add that include in a bunch of places, but it looks like it's only needed in `ConstantFolder.h` & `IRBuilderFolder.h` (still building ...)

I'll update this PR to only have it in the appropriate headers.

https://github.com/llvm/llvm-project/pull/94580