Fix emulators/virtualbox-ose build after r552109.

VirtualBox embeds an outdated version of glext.h, causing it to
fail to build due to symbols being redefined incorrectly.

Import patch which forces virtualbox to append it's own include
paths, thus not "obscuring" the system provided OpenGL include file.

PR: 250315
Submitted by: rozhuk.im@gmail.com
Approved by: portmgr (fixit blanket)