This directory was generated from the mesa-7.2.tar.gz archive by unpacking it
and executing

$ mkdir $VBOX_PATH/src/VBox/Additions/x11/x11include/mesa-7.2
$ cp -r include/GL $VBOX_PATH/src/VBox/Additions/x11/x11include/mesa-7.2

in the mesa-7.2 directory.