[index] Don't add relation to a NamedDecl with no name

Unless it's one of the special cases (tag, category) that we can handle.
This syncs up the check between handling a decl and handling a relation.

This would cause invalid nameless decls to end up in relations despite
having no name or USR.

rdar://problem/32474406

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@307855 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed