llvm.swift.async.context.addr cannot be modeled as NoMem because we don't want...

llvm.swift.async.context.addr cannot be modeled as NoMem because we don't want it to be cse'd accross async suspends

An async suspend models the split between two partial async functions.
`llvm.swift.async.context.addr ` will have a different value in the two
partial functions so it is not correct to generally CSE the instruction.

rdar://97336162

Differential Revision: https://reviews.llvm.org/D130201