[clang] [llvm] [AMDGPU][WIP] Add support for i64/f64 readlane, writelane and readfirstlane operations. (PR #89217)

[Jay Foad via cfe-commits]

jayfoad wrote:

Previous attempts:
* https://reviews.llvm.org/D84639
* https://reviews.llvm.org/D86154
* https://reviews.llvm.org/D147732
* #87334

https://github.com/llvm/llvm-project/pull/89217