SDL2: Always --disable-x11-shared so X11 is linked the normal way.

This fixes creating a GL context with r600_dri (and probably other drivers)
on NetBSD with native X, where otherwise missing libxcb symbol errors
happen.

Programs this unbreaks include fasttracker2, mednafen. Programs this
doesn't unbreak include nestopia (uses libepoxy).

This is a workaround, but we're already doing the same in the SDL1
package...

Bump PKGREVISION.

(nia)