[m-rev.] for review: Support building Boehm GC with Winpthreads.

[Julien Fischer]

On Wed, 13 Aug 2014, Peter Wang wrote:

> Branches: master, 14.01
>
> Winpthreads is a pthreads implementation from the MinGW-w64 project,
> different from pthreads-win32.  A similar patch to this should make its
> way into Boehm GC upstream.  As we will not be upgrading Boehm GC on the
> 14.01 branch, apply this small change to our copy of the library for now.
>
> boehm_gc/include/private/gc_locks.h:
> 	Winpthreads uses scalar thread IDs.
>
> boehm_gc/win32_threads.c:
> 	Winpthread thread IDs should be virtually unique but make the
> 	conservative assumption anyway.

That's fine.

Cheers,
Julien.