[DIBuilder] Make createReferenceType take size and align

Summary: Since we're passing references to dbg.value as pointers,
we need to have the frontend properly declare their sizes and
alignments (as it already does for regular pointers) in preparation
for my upcoming patch to have the verifer check that the sizes agree.

Also augment the backend logic that skips actually emitting this
information into DWARF such that it also handles reference types.

Reviewers: aprantl, dexonsmith, dblaikie

Subscribers: dblaikie, llvm-commits

Differential Revision: http://reviews.llvm.org/D14275

llvm-svn: 253186