llvm-dwarfdump: Add support for some COFF relocations

DWARF in COFF utilizes several relocations.  Implement support for them
in RelocVisitor to support llvm-dwarfdump.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219280 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed