This is primarily used for reading debug info from unrelocated object files, for handling addr and secrel relocations.
Also add testcases for the existing code for COFF on X86.
@JDevlieghere - I'm adding tests for this under tools/llvm-dwarfdump. Currently there's two subdirs, X86 and AArch64 there, while I'm adding four testcases (coff-i386, coff-x86_64, coff-arm and coff-arm64). Are you ok with them placed in the toplevel dir, or do you want a different structure for them?