[codeview] Translate basic DITypes to CV type records

Summary:
This is meant to be the tiniest step towards DIType to CV type index
translation that I could come up with. Whenever translation fails, we use type
index zero, which is the unknown type.

Reviewers: aaboud, zturner

Subscribers: llvm-commits, amccarth

Differential Revision: http://reviews.llvm.org/D20840

llvm-svn: 271408