[m-rev.] for review: Account for Winpthreads in configure.

[Peter Wang]

On Wed, 13 Aug 2014 15:01:00 +1000 (EST), Julien Fischer <jfischer at opturion.com> wrote:
> 
> On Wed, 13 Aug 2014, Peter Wang wrote:
> 
> > Branches: master, 14.01
> >
> > configure.ac:
> > 	Always build Boehm GC with GC_WIN32_PTHREADS when pthread.h is
> > 	detected on MinGW* systems.
> 
> Even in non par grades when parallel marking is not enabled?  What
> pthreads calls could we make then then?   I think libc on MinGW-w64
> requires winpthread to support some C11 features, so maybe it's always
> needed on that system, but shouldn't it remain possible to build non
> .par grades on plain MinGW without requiring pthreads?

I guess it wasn't clear that it only affects .par grades and the par_gc
library.  New description:

configure.ac:
        Always build the par_gc library with GC_WIN32_PTHREADS when
        pthread.h is detected on MinGW* systems.  Previously, if the
        pthread implementation is not pthread-win32 we would fallback to
        building Boehm GC with GC_WIN32_THREADS (no "P"), so it would
        NOT provide pthread wrapper functions.  But since pthread.h was
        found the Mercury implementation would make pthread calls, calls
        which are not intercepted by Boehm GC, and thus unsafe.

Peter