swift234

[ClangImporter] Don't include Swift members in AnyObject lookup. (#2503)

More specifically, don't include declarations of methods and properties
in the list of "all imported Objective-C members" if said method or
property is in a generated header. (We actually key off of whether the
enclosing class, protocol, or category is marked as coming from Swift,
but since users aren't supposed to modify generated headers themselves
it's much the same thing.)

This previously caused a crash because we tried to import a Clang member
onto a Swift decl in order to provide the particular member on AnyObject.

rdar://problem/25955831 and probably also rdar://problem/25828987, which
deals with the fix-it to migrate to #selector. (We do an AnyObject-like
lookup to find out which class likely implements the specified selector.)