If a C++ `struct Base` declares a method with a Clang attribute that Swift is able to import, and `struct Derived` inherits from `Base`, the method should get cloned from `Base` to `Derived` with its attributes.
Previously we were only cloning one attribute at most due to a bug in `cloneImportedAttributes`. DeclAttributes is an intrusively linked list, and it was being made invalid while iterating over it: `otherDecl->getAttrs().add(attrs)` iterates over the list and calls `otherDecl->add(eachElement)`, which invalidates the iterator after the first iteration.
We do not synthesize the inheritance thunks correctly for such methods. Do not try to synthesize them, as that causes issues when there are two overloads of the same method, one with rvalue this and one without.
The proper solution is tracked as https://github.com/apple/swift/issues/69745
Unblocks rdar://114282353
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.
Trying to use members of C++ private base classes from Swift causes an assertion failure in ClangImporter:
```
<build dir>/swift/lib/swift/macosx/arm64/libcxxshim.h:2:66: error: cannot cast 'A' to its private base class 'B'
To __swift_interopStaticCast(From from) { return static_cast<To>(from); }
^
```
Such members should not be exposed.
rdar://103871000
This commit adds very basic support for importing and calling base class methods, getting and setting base class fields, and using types inside of base classes.
