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

[Alex Bradbury via llvm-commits]

asb wrote:

Sorry for the delay, I was away on holiday. I've rebased, precommitted the example I used in the original description, and updated the affected tests in llvm/test/Transforms/LoopStrengthReduce/RISCV that were missed in the first patch.

@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.

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