swift234

Always track external decls, not just during name binding and type checking.

LLDB creates variables that have types before name binding and type checking
actually occur, and this can bring in types from the Clang importer...which
then don't satisfy the constraints of a valid AST. Make sure we always get
a shot at checking these decls.

No test case, unfortunately, but LLDB should have one in their test suite
once this goes in.

<rdar://problem/15838120>

Swift SVN r12686