DebugInfo: Unify & optimize the lazy addition of record types

Rather than going through the whole getOrCreateType machinery to
manifest a type, cut straight to the implementation because we know we
have to do work.

While the previous implementation was sufficient for the two cases
(completeness and required completeness) we have already (the general
machinery could inspect the type for those attributes & go down the full
definition path), a pending change (to emit info for types when we emit
their vtables) won't have that luxury & we'll need to force the creation
rather than relying on the general purpose routine.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@188486 91177308-0d34-0410-b5e6-96231b3b80d8