These are the remaining build files needed for building lld. Mostly boring.
The diff in targets.gni is due to me running gn format on all gn(i) files.
llvm_enable_dia_sdk is in a gni file because I'm going to have to read it when writing the lit invocations for check-llvm and check-lld. I've never had the DIA sdk installed locally so I never tested building with it enabled -- it probably doesn't Just Work and needs some path to diaguids.lib. We can finish that once somebody needs it.