Bison 2.1 on win32

I just tried building with Bison 2.1 on msvc, and it broke. For one
thing, the .BAT file rejects 2.1 as broken instead of 2.0, which is
obviously incorrect :-)

But the generated C file also does not compile causing the error on
http://msdn2.microsoft.com/en-us/library/93az0868.aspx, because msvc
doesn't define __STDC__, which causes Bison to generate code it can't
compile. Defining __STDC__ globally breaks several other places, since
it affects a lot of include files that aren't necessarily others.

The attached patch seems to fix the build issue. Does it seem
acceptable/the right thing to do?

Another option would be to just reject both 2.0 and 2.1 as broken to
build pg with, I guess...

//Magnus