support vbox 7.0.18 and 7.0.20

[blabla-my]

Tested by following commands:

$ docker build -t videzzo .
$ docker run --rm -it \
    -v /usr/src:/usr/src \
    -v /dev:/dev \
    -v /lib/modules:/lib/modules \
    --privileged \
    -v $PWD:/root/videzzo videzzo:latest \
    /bin/bash
# in container 
$ cd videzzo && make vbox
$ bash -x videzzo_tool/04-quick-cov.sh qemu i386 ac97 60

This patch involves modifications on CLANG.kmk and vbox source code patch (videzzo_vbox/0001-Update-VBOX-to-support-ViDeZZo-as-a-library.patch). For CLANG.kmk, addprefix should be replaced with qaddprefix to avoid error of double qoutes.

This patch does not work on vbox <=7.0.4 and vbox >7.0.20 . May consider not to merge into main stream immediately.