So, for the basics, i’d suggest you check you have all the development tools.
Since AUR helpers are not officially supported for building AUR packages, you should also try building and installing manually: Arch User Repository - ArchWiki
On a side node, a thing that ticks me is that the error points to a file within your home. Since you installed virtualenv through the package manager, i’d rather expect the build process to use the one from the system…