[llvm] [CHERI] Refine LoopIdiomRecognize handling of non-integral pointers. (PR #189402)

[Owen Anderson via llvm-commits]

resistor wrote:

> This looks sensible to me but we should get approval from AMDGPU folks here due to the conversion of nullptr stores to memset. @arsenm @shiltian

I hope that something akin to https://github.com/llvm/llvm-project/pull/183215 will eventually land, which should compose with this change to allow us to get the whichever behavior each target wants.

https://github.com/llvm/llvm-project/pull/189402