[llvm] [X86][GlobalIsel] Add ceil/trunc/floor cpp intrinsic test (PR #156281)

[Simon Pilgrim via llvm-commits]

https://github.com/RKSimon requested changes to this pull request.

Just call them isel-ceil.ll / isel-floor.ll / isel-ftrunc.ll - the llvm from the intrinsic name is redundant for something as generic as this.

https://github.com/llvm/llvm-project/pull/156281