[DWARFv5] Update definitions to match published spec.

Some late additions to DWARF v5 were not in Dwarf.def; also one form
was redefined.  Add the new cases to relevant switches in different
parts of LLVM.  Replace DW_FORM_ref_sup with DW_FORM_ref_sup[4,8].

I did not add support for DW_FORM_strx3/addrx3 other that defining the
constants. We don't have any infrastructure to support these.

Differential Revision: http://reviews.llvm.org/D30664

llvm-svn: 297085