DWARF parser: Fix DWARF-2/3 incompatibility: size of DW_FORM_ref_addr is the same...

DWARF parser: Fix DWARF-2/3 incompatibility: size of DW_FORM_ref_addr is the same as DW_FORM_addr in DWARF2, and is 4/8 bytes on 32/64-bit DWARF starting from DWARF3. Adding a test for this is a huge pain - generating and uploading pre-built binary with DWARF3 debug info is way too ugly, and writing fine-grained unittests for DebugInfo is impossible, as it doesn't expose any headers in include/llvm. That said, I'm going to choose the second approach and submit the patch exposing DebugInfo headers for review soon enough.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179095 91177308-0d34-0410-b5e6-96231b3b80d8