[llvm] [Float2Int] Resolve FIXME: Pick the smallest legal type that fits (PR #79158)

[Jessica Clarke via llvm-commits]

jrtc27 wrote:

Compiler Explorer shows this bug as being reproducible with that exact test case all the way back to Clang 3.7 (but not 3.6). Given Float2Int was new in 3.7 (at least from GitHub's view of available tags) that strongly suggests to me this bug has always been there since it was added to the tree (or at least the final attempt at adding it to the tree).

https://github.com/llvm/llvm-project/pull/79158