[llvm] [SelectionDAG][X86] Add floating point promotion. (PR #118793)

[via llvm-commits]

jofrn wrote:

This commit, which contains a target-dependent X86 change, is based on
1. https://github.com/llvm/llvm-project/pull/117625, which contains enabling of atomic vector types in IR/Verifier
2. https://github.com/llvm/llvm-project/pull/111414, which contains target-independent scalarization of atomic load vector.

https://github.com/llvm/llvm-project/pull/118793