boehm-gc: win32 getenv support, Tru64 cleanup

["Boehm, Hans" <hans_boehm at hp dot com>]

Oyvind pointed out that environment variables currently can't be used to
influence the GC on win32.  This makes it significantly harder to 
diagnose and possibly work around problems such as 

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=10746

The reason getenv was disabled on win32 is given in

http://gcc.gnu.org/ml/java-patches/2002-q1/msg00701.html

(Based on some experiments on win32 and a quick look at the C89 standard,
the Wine behavior described in that message is clearly wrong.)

Does anyone know if the Wine bug that caused all this still exists?

Assuming it does, the attached patch (only partially tested without Wine)
should work around the problem while making environment variables usable
on win32.  The patch has the unpleasant side effect of treating environment
variables with empty definitions as undefined environment variables under
win32, but my impression is that is far more tolerable than the current
situation. If someone could test this with mingw32 and ideally Wine, that
would be appreciated.

The attempt to generate this patch pointed out that I had some OSF1/Tru64
configury stuff in my tree that apparently was never checked into CVS.
I left it in below.  Is there a reason not to check this in?  It is in the
standalone version of the GC.

Hans

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