[llvm] [RISCV] Enable TTI::shouldDropLSRSolutionIfLessProfitable by default (PR #89927)

[Philip Reames via llvm-commits]

preames wrote:

> @preames I think you wrote the affected LoopStrengthReduce/RISCV tests - I just wanted to reconfirm you're happy with the test changes shown in these files, and if you think any additional comments should be added.

The reasoning from my early LGTM still applies.  I glanced at the LSR changes, and see a couple of regressions, but I still think the right path forward is to enable this and then iterative improve.  

https://github.com/llvm/llvm-project/pull/89927