.In this patch, I flip the switch in DriverUtils from using the externalcvtres.exe tool to using the Windows Resource library in llvm.I also fixed a bug where .rsrc sections were marked as discardable
memory and therefore were placed in the wrong order in the final PE.
Furthermore, I modified WindowsResource to write the coff directly to a
memory buffer instead of to file, also had it use the machine types
already declared in COFF.h instead creating my own enum.
Changed WindowsResourceCOFFWriter to write to a memory buffer instead of file. Also got rid of my own Machine enum and use the one defined in COFF.h
Either make this a reference or a pointer, but not a reference to a unique_ptr. Probably a reference is fine since it doesn't make sense to write something without a valid output buffer.