[clang] [llvm] [X86] Fix x87 excess precision escaping into f32/f64 values (PR #215104)

[Trevor Gross via cfe-commits]

tgross35 wrote:

GH has a terrible UI for per-commit review and it's useful to have the specific commit messages in history, so IMO it's worth splitting now. Also worth knowing that the NFC test additions actually pass in CI before they are updated.

But I'm also not an LLVM maintainer and have no idea if the approach here is reasonable.

https://github.com/llvm/llvm-project/pull/215104