The `-Winvalid-offsetof` warning is valid in this case. `offsetof` is
being applied to types with a non-standard layout. The layout of this
type is undefined by the specification. There is no guarantee that the
type layout is uniform across all ABIs. It is not possible to portably
compute the offset statically, especially efficiently.
Sink this check into a unit test to avoid performing this test at
runtime. In order to do this in the standard library, we would need to
do this check through a global constructor.
We were missing a field in `SwiftJob`, which broke various things. To
avoid that problem in future, this PR adds a set of static asserts to
check the layout of various structures and that we're using the same
values as well.
Also added some functions to the ABI, and fixed things so that if you
enable the debug logging the library still builds (there was an extra
`_` in `Actor.cpp` that caused a build failure).
Finally, renamed `Hooks.cpp` to `ConcurrencyHooks.cpp`.
rdar://135380149
