[clang] [llvm] Reimplement constrained 'trunc' using operand bundles (PR #118253)

[Serge Pavlov via cfe-commits]

spavloff wrote:

### Merge activity

* **Dec 2, 12:55 AM EST**: The merge label 'FP Bundles' was detected. This PR will be added to the [Graphite merge queue](https://app.graphite.dev/merges?org=llvm&repo=llvm-project) once it meets the requirements.


https://github.com/llvm/llvm-project/pull/118253