[clang] [Clang] Use ConstantExpr::getGetElementPtr() with DataLayout (PR #225415)

[Nikita Popov via cfe-commits]

nikic wrote:

CIR tests need to be updated in similar ways to the Clang tests updated in this PR. I don't plan to do this myself (CIR is a peripheral tier component, so it's the responsibility of CIR maintainers to resolve any issues).

https://github.com/llvm/llvm-project/pull/225415