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

[Matt Arsenault via cfe-commits]

arsenm wrote:

> Two, we can add a "readnone_fp_intrinsic" attribute, which would mean the intrinsic is readnone unless there's an operand bundle indicating otherwise.

I think this needs to be more refined to FP mode read/write and errno read/write. Basically a mirror of memory() for arguments/other memory 

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