Note that llvm::support::endianness has been renamed to
llvm::endianness while becoming an enum class as opposed to an
enum. This patch replaces support::{big,little,native} with
llvm::endianness::{big,little,native}.
Set ups the infrastructure to create an empty GOFF file.
Also adds a GOFF writer which writes only HDR/END records.
Reviewed By: jhenderson, kpn
Differential Revision: https://reviews.llvm.org/D111437