Cross compile QT 5.8 for Beaglebone Black

I am really new in this.
I trying to configure Qt to use with the Beaglebone by Cross-compile
I followed some step from several tutorials, but some links are down or are so old, and I get some errors.
I want to compile QT 5.8 because I need to use the Modbus library, But I dont know how to start to set up
1.- I have a computer where I have installed Ubuntu 16.04 on a virtual machine using virtualbox.
2.- I downloaded the lasted toolchain and the sysroot from linaro (gcc 4.9)
3.- My Beaglebone has the image from the oficial page bone-debian-8.6-lxqt-4gb-armhf-2016-11-06-4gb.img.xz

Can anyone help me by telling me what I have to do to achieve it?