obj2yaml: Use the correct relocation type for different machine types

The IO normalizer would essentially lump I386 and AMD64 relocations
together.  Relocation types with the same numeric value would then get
mapped in appropriately.

For example:
IMAGE_REL_AMD64_ADDR64 and IMAGE_REL_I386_DIR16 both have a numeric
value of one.  We would see IMAGE_REL_I386_DIR16 in obj2yaml conversions
of object files with a machine type of IMAGE_FILE_MACHINE_AMD64.

llvm-svn: 205746