Debug Info: according to DWARF 2, FORM_ref_addr the same size as an address on
the target system.

It was hard-coded to 4 bytes before. I can't get llvm to generate a
ref_addr on a reasonably sized testing case.

rdar://problem/13559431


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178722 91177308-0d34-0410-b5e6-96231b3b80d8