-ObjC is still not always generated when linking static xcframeworks

[paulb777]

#10234 turns out to be an incomplete fix.

https://github.com/fthdgn/firebase-ios-sdk-issue-7595 demonstrates an example of a necessary -ObjC not being generated. Full explanation firebase/firebase-ios-sdk#7595 (comment).

Debugging shows the new builld_settings code added in #10234 only executed for aggregate targets and exiting early because of no response to :vendored_xcframeworks.

Unfortunately, I lost track of the test case I used with #10234 and I'm not sure what's different about the working and non-working cases.