glx: revert using nonexsisten XCB version of glXGetFBConfigsSGIX

This uses a GLX VendorPrivate request. VendorPrivates are real GLX API
calls but use the same protocol request. XCB does not currently
support specific VendorPrivetes directly. See eg.:
http://lists.freedesktop.org/archives/xcb/2008-November/004036.html
for more information.
1 file changed