Migrate the DWARF_VERSION constant to 4. It largely needs to go away.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189824 91177308-0d34-0410-b5e6-96231b3b80d8
[MC] Revert part of my previous change, I was a bit overzealous.

A change to test the previous commit will be coming soon.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@189825 91177308-0d34-0410-b5e6-96231b3b80d8