Debug Info: revert 178722 for now.

There is a difference for FORM_ref_addr between DWARF 2 and DWARF 3+.
Since Eric is against guarding DWARF 2 ref_addr with DarwinGDBCompat, we are
still in discussion on how to handle this.

The correct solution is to update our header to say version 4 instead of version
2 and update tool chains as well.

rdar://problem/13559431

llvm-svn: 178806