RX Vega + Ubuntu 16.04.3 = no OpenCL

[pluna]

I don't know if you are new to Linux so forgive me if you have already done all this, but did you try to download the source and build locally?

Open a terminal and create a build directory and then cd into that directory.
mkdir /home/YOUR_USER_NAME/hashcat
cd /home/YOUR_USER_NAME/hashcat

You might need to install git before the following will work.
sudo apt-get install git

Then type the following commands:
git clone https://github.com/hashcat/hashcat.git
cd hashcat
git submodule update --init
make

Then you can try running it before installing it:
./hashcat -b

I can't remember if there are any dependencies that I needed to download with apt-get. Anyway, try the above and get back to me.