Reapply "DebugInfo: Omit class definitions even in the presence of available_externally vtables"

Accounts for a case that caused an assertion failure by attempting to
query for the vtable linkage of a non-dynamic type.t

This reverts commit r292801.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@293462 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed