Port the error functions from ELF to COFF.

This has a few advantages

* Less C++ code (about 300 lines less).
* Less machine code (about 14 KB of text on a linux x86_64 build).
* It is more debugger friendly. Just set a breakpoint on the exit function and
  you get the complete lld stack trace of when the error was found.
* It is a more robust API. The errors are handled early and we don't get a
  std::error_code hot potato being passed around.
* In most cases the error function in a better position to print diagnostics
  (it has more context).

llvm-svn: 244215