[llvm] TTI: Check legalization cost of fptosi_sat/fptoui_sat nodes (PR #100521)

[Matt Arsenault via llvm-commits]

arsenm wrote:

### Merge activity

* **Aug 9, 4:27 AM EDT**: @arsenm started a stack merge that includes this pull request via [Graphite](https://app.graphite.dev/github/pr/llvm/llvm-project/100521).


https://github.com/llvm/llvm-project/pull/100521