[llvm] [RISCV] Enable store clustering by default (PR #73796)

[Philip Reames via llvm-commits]

https://github.com/preames approved this pull request.

LGTM

I have skimmed (most of) the tests, and see nothing concerning.

I do see a couple possibilities for store merging, but that's an entirely different topic.  For later consideration, the two interesting sub-cases I noticed are: both are storing zero, and we have zbkb.  

https://github.com/llvm/llvm-project/pull/73796