Windows logic for determining address-only type layout for a C++ type is now unified with other platforms.
However, this means that on Windows, a C++ type with a custom destructor, but a default copy constructor
is now loadable, even though it's non-trivial. Since Swift does not support such type operations at the
moment (it can't be yet destroyed), mark such type as unavailable in Swift instead, when building for
the Windows target.
This fixes the Windows miscompilation related to such types when they were passed indirectly to C++
functions even though they're actually passed directly.
This patch adds support for custom C++ destructors. The most notable thing here, I think, is that this is the first place a struct type has a custom destructor. I suspect with more code we will expose a few places where optimization passes need to be fixed to account for this.
One of many patches to fix SR-12797.
