DOS .exe stack size patching: Ensure to always write 32bit

fbGetOption() returns an Integer, which becomes 64bit on 64bit.
64bit: Add support for ThreadCall
gfxlib2: Fix dangling pointer in X11 OpenGL driver_init() (fixes #713)

The dpy pointer was static, and could be re-used by secondary
driver_init calls. However it was also assigned to fb_x11.display,
which is cleaned up by fb_hX11Exit(). That leaves the dpy pointer
dangling, causing problems on any further X11 OpenGL screen
initialization. Thus every time an X11 OpenGL screen was closed, and a
new one opened, the program would access a dangling pointer.

This partially reverts 7d03abf8; hopefully it's reintroducing the
problem solved there.

The changes to fb_hX11Exit() seemed necessary in case the X11 OpenGL
driver_init() exits due to an error but after setting fb_x11.display.
Then fb_hX11Exit() may be called without fb_hX11Init() having been
called. In that situation, any previous fb_hX11Exit()'s had better not
left any dangling pointers sitting in those global vars, otherwise
there would be double frees now.