[clang] [llvm] [LLVM][IR] Add native vector support to ConstantInt & ConstantFP. (PR #74502)

[Paul Walker via cfe-commits]

paulwalker-arm wrote:

The PR contains a couple of commits that unless there's disagreement I'm tempted to land directly but have held off just in case there's any buyer remorse about extending ConstantInt/ConstantFP to cover vector types.

For similar reasons I've not updated the LangRef as I don't really want people using the support until at least code generation works.

https://github.com/llvm/llvm-project/pull/74502