[clang] [llvm] [Headers][X86] Allow vector bitcast intrinsics to be used in constexpr (PR #167180)

[Simon Pilgrim via llvm-commits]

RKSimon wrote:

@Red-RobinHood are you still able to work on this? Ideally we should be getting most of the constexpr intrinsics work done this month in prep for the next release.

https://github.com/llvm/llvm-project/pull/167180