Fix lib/Basic Windows/Cygwin build

[hughbe]

The problem here is that TaskQueue::addTask has an optional parameter SeparateErrors that isn't included in lib/Basic/Default/TaskQueue.inc. As such, we get overloaded member function not found in 'swift::sys::TaskQueue' errors compiling the Swift project on Windows/Cygwin

We never noticed this due to the following code

#if LLVM_ON_UNIX && !defined(__CYGWIN__)
#include "Unix/TaskQueue.inc"
#else
#include "Default/TaskQueue.inc"
#endif

[CodaFi]

/CC @matthewcarroll who is working in this area. I wonder if this fix can be folded into that patch.

[matthewcarroll]

@CodaFi,

Yes, would you like me to merge this branch into mine?

[CodaFi]

If you wouldn't mind, thanks!

[matthewcarroll]

@CodaFi done

[hughbe]

Should I close this then