Hi Guix,

wabt includes tools for manipulating WebAssembly/Wasm related files.

Does web.scm make sense for it? 

I'm sure better formatting could be done on the synopsis and
description... help would be appreciated!

This also adds yet another test suite dependency and optional feature
for diffoscope; not sure if that should be in a separate patch; in this
case I've added it in the same commit...

Thanks!

live well,
  vagrant