Support for LLVM memoryeffects attribute

[wsmoses]

With readonly/readnone/writeonly being no longer permissible as llvm fn args in later LLVM's a nice way to query for this would be helpful

[maleadt]

Needs something like llvm/llvm-project#75123 but for setMemoryEffects/getMemoryEffects.

[wsmoses]

Enzyme.jl now vendors its own version of this here to be able to not crash on 1.11: https://github.com/EnzymeAD/Enzyme.jl/blob/e9804331d9e5ef6c277982e68f9077203b6d1a37/src/compiler/utils.jl#L1

Happy to have that brought in upstream here.