[PATCH 0/2] Implement target async for Windows

[Tom Tromey <tromey@adacore.com>]

I wanted target async to work on Windows for another project.  This
short series is the result.

This series is based on my earlier patch to make strwinerror available
to all the Windows native code.  That patch was useful while debugging
these.

The basic problem on Windows is that WaitForDebugEvent can't be mixed
with WaitForMulpleObjects -- there's no way to get some kind of "debug
handle" to wait on.  To handle this, WaitForDebugEvent is now called
in a worker thread.  However, to do that, certain other Windows calls
must be done in that same thread, as various debugging APIs can only
be used from the thread that started the inferior.  (Not all of these
are documented, either.)

I've tested this using the internal AdaCore test suite.

Tom