[llvm] CallPromotionUtils: Correctly use IndexSize when determining the bit width of pointer offsets. (PR #119483)

[Owen Anderson via llvm-commits]

resistor wrote:

> > jrtc
> 
> jrtc27 (or my name)

Done, though I had to squash and rewrite history, which may make the PR reviews a bit hard to follow.

https://github.com/llvm/llvm-project/pull/119483