This removes all support for GC mode.
This was deprecated by Apple in OS X 10.8 (2012) and never supported in
iOS. Very little code ever tried to use it with this runtime.
It's gone from the build system already.
On 32-bit Windows, malloc doesn't give us memory with sufficiently
strong alignment for AVX vectors.
Note that Windows also has a family of allocators that provide guarantee
exact misalignment. Using these would simplify the ivar layout logic
slightly, because we wouldn't need to account for the refcount pointer.
It's not clear that it's actually worth doing though, because that logic
already exists.
- __strong pointers, preventing objects from being freed
_ __weak pointers are automatically freed when the last remaining __strong pointer goes away
- objc_gc_{retain,release}_np() functions, which can be used to implement CFRetain() and CFRelease() (adds an reference count - the object will not be collected until after its last retain is gone.
David Chisnall
theraven