Compilation warning: unused-function

[jordanmontt]

If one compiles the VM with the warning Wno-unused-function (Remove the warning form the list in the CMake file) there are a lot of warnings. There are two types:

1. The warnings from the extracted plugins
2. The warnings from generated slang code

The 1 is trivial to fix. To do it, one needs to go to the extracted folder in this repo and remove the functions by hand. There is a first PR that removed lots of unused functions: #780 But, there are still warnings. At least 400 of them after the PR gets merged.

The 2 one is more complicated. It requires to change Slang. I will open another issue for this.