[llvm] [BasicTTIImpl] Add cost entries for ldexp, [l]lround (PR #146373)

[Ramkumar Ramachandra via llvm-commits]

artagnon wrote:

> providing that the SVE tests still produce an invalid cost. (We will need to add lowering)

This checks out.

https://github.com/llvm/llvm-project/pull/146373