Ok so my suspicion was right that you indeed have compilation errors which were not revealed by axbuild, and preventing CIL compilation.
Those classes are using .Net assembly references. You might have the wrong .Net framework, or an installation/Windows update could have broken it.
You could try to re-install the .Net framework required for the AX version you have, check it in the System requirements guide.
If you are unable to fix it, since you are talking about a Dev workspace, try doing a fresh install from a newly created Windows virtual machine, and installing pre-requisites, then putting AX on top.