swift234

[ClangImporter] Don't attach Clang decls to defined-in-Swift classes.

(and protocols)

I had missed this check before. It probably made very little difference, but
we use "hasClangNode" to mean "defined-in-Objective-C", so it's better to get
this correct.

The test change is fairly minimal: not giving the class a Clang node means we
have to find it by lookup, but the Objective-C part of the "Base" module
wasn't actually considered visible by Clang. In a real situation the "Base"
module would be a proper framework and both halves of the module would have
been imported, as tested by the mixed-language test.

Swift SVN r15248