Import LLVM.Interop functionality

[maleadt]

As part of LLVM.jl 5, I'm removing the atomics-related functionality that was added to the LLVM.Interop module in maleadt/LLVM.jl#308. The functionality has some issues (@dynamic_order generating code for all cases is invalid, e.g., AtomicRMW cannot be used with Unordered and causes an abort on LLVM 15), but in hindsight I also think that it doesn't really belong in LLVM.jl which provides lightweight wrappers around the LLVM APIs, and by extension some functionality to interface with Julia's LLVM support (i.e. llvmcall, LLVMPtr, etc).

This change wont break UnsafeAtomicsLLVM.jl because it's part of the breaking LLVM 5.0 release, but opening an issue so that it's clear that this code needs to be imported here before bumping the compat bounds: https://github.com/maleadt/LLVM.jl/blob/ba3d82d56a789bd0c48f372be38ae52407372f2f/src/interop/atomics.jl

[vchuravy]

Partially done in #8