[llvm] CallPromotionUtils: Correctly use IndexSize when determining the bit width of pointer offsets. (PR #119138)

[Alexander Richardson via llvm-commits]

arichardson wrote:

> > Looks like this is my downstream commit [CTSRD-CHERI/llvm-project at fb9fa37](https://github.com/CTSRD-CHERI/llvm-project/commit/fb9fa3765325776d07c547b1b0668e6c749120f3), would be nice if you could add `Co-authored-by:`.
> 
> Sure. Is that just written into the commit message, or do I need to do something special to make git recognize it?

Just needs to be a separate line in the commit message [for github to recognize it](https://docs.github.com/en/pull-requests/committing-changes-to-your-project/creating-and-editing-commits/creating-a-commit-with-multiple-authors). I believe I was still at Cambridge Uni back then so adding
`Co-authored-by: Alexander Richardson <alexander.richardson at cl.cam.ac.uk>` would be correct.

https://github.com/llvm/llvm-project/pull/119138