BitcodeReader: Fix some holes in upgrade from r267296

Add tests for some missing cases to bitcode upgrade in r267296.

  - DICompositeType with an 'elements:' field, which will cause it to be
    involved in a cycle after the upgrade.

  - A DIDerivedType that references a class in 'extraData:'.

I updated test/Bitcode/dityperefs-3.8.ll with the missing cases and
regenerated test/Bitcode/dityperefs-3.8.ll.bc.

llvm-svn: 267332