[Xcb] patch Windows port

[Vincent Torri]

Hey,

> Thanks for the patch. I'd like to apply and test this against the current xcb
> tree. Is this patch intended for building and installing xcb using msys/mingw,
> will it work if I cross compile using mingw?....or I have I completely
> misunderstood the intent of this patch?

the patch tells libtool that we build a DLL on Windows, export names 
correctly (though we should use a macro like XAPI that should be in front 
of all function declaration) and install xcb_windefs.h if we are on 
Windows.

It will work natively (on Windows) or when cross-compiling.

Vincent