importer::findOptionSetEnum() uses some fragile heuristics to determine
whether a typedef is involved in the construction of a CF_OPTIONS or
NS_OPTIONS type. This patch adds an explicit check that the typedef is
expanded from either of those macros, to prevent, e.g., an unavailable
NS_ENUM, from being mistakenly recognized as an NS_OPTIONS.
Note that doing this is still kind of fragile, and prevents users from
building {NS,CF}_OPTIONS with their own macros. The right thing to do is
probably specifically look for the flag_enum attribute, but that is not
currently what we're doing for reasons whose discovery is left as
an exercise to the future git archaeologist.
This patch also removes (part of) a test case that builds
a CF_OPTIONS-like type with the "SOME_OPTIONS" macro, which is no longer
supported as of this patch.
rdar://150399978
This removes a workaround from the module interface loader, which was forcing AppKit and UIKit to be rebuilt from their textual interfaces with C++ interop disabled, even if the current compilation explicitly enables it.
The workaround was previously put in place because of a compiler error:
```
error: type 'AttributeScopes.AppKitAttributes.StrikethroughStyleAttribute' does not conform to protocol 'AttributedStringKey'
note: possibly intended match 'AttributeScopes.AppKitAttributes.StrikethroughStyleAttribute.Value' (aka 'NSUnderlineStyle') does not conform to 'Hashable'
```
`NSUnderlineStyle` is a C/C++ type from AppKit that is declared using `NS_OPTIONS` macro. `NS_OPTIONS`/`CF_OPTIONS` macros have different expansions in C vs C++ language modes. The C++ expansions weren't handled correctly by ClangImporter, resulting in two distinct Swift types being created: a `typealias NSUnderlineStyle` which was marked as unavailable in Swift, and `enum NSUnderlineStyle`. This mostly worked fine, since the lookup logic was picking the enum during regular name lookup. However, this silently broke down when rebuilding the explicit conformance from `AppKit.swiftinterface`:
```
extension AppKit.NSUnderlineStyle : Swift.Hashable {}
```
Swift was picking the (unavailable) typealias when rebuilding this extension, which means the (available) enum wasn't getting the conformance.
This is verified by an existing test (`test/Interop/Cxx/objc-correctness/appkit-uikit.swift`).
rdar://142961112
