[clang] [CIR] Add cir.signbit to tablegen (PR #184091)

[Akimasa Watanuki via cfe-commits]

Men-cotton wrote:

@YeonguChoe 
Please stop repeatedly clicking the merge with main button. It floods the notification thread.

LLVM merges hundreds of PRs into "main" every day (see https://github.com/llvm/llvm-project/commits/main/), so rebasing or merging with "main" on every update is unnecessary. Only do this when an actual merge conflict appears.

There are already review comments on this PR. Please focus on addressing those first. If you are unsure how to interpret or respond to the reviews, feel free to ask questions.

https://github.com/llvm/llvm-project/pull/184091