b08837f180
only set noalias on Box with the global allocator As discovered in https://github.com/rust-lang/miri/issues/3341, `noalias` and custom allocators don't go well together. rustc can now check whether a Box uses the global allocator. This replaces the previous ad-hoc and rather unprincipled check for a zero-sized allocator. This is the rustc part of fixing that; Miri will also need a patch.