[llvm] [clang] [IR] Fix GEP offset computations for vector GEPs (PR #75448)

[Jannik Silvanus via cfe-commits]

jasilvanus wrote:

> Can this solve #68566 too?

I don't think it solves it, as it only fixes offset computations within GEPs and doesn't teach code in general about the correct vector layout. However, it is reducing the amount of code assuming the wrong layout.

There seem to be some clang test failures though that I'm currently looking into.

https://github.com/llvm/llvm-project/pull/75448