hi lpvmc, welcome to LinuxQuestions.
the SlackBuilds scripts are meant to be run from a Slackware operating system as they make certain assumptions on the software installed on your host: the error you got is because your o.s. doesn't have pkgtools installed.
I'm not a Mint user but looking
here I can assume pysolfc should be available in Mint's repositories: if you want to install a software on your distribution you better check first if it's available in its own repos...
as this is a forum dedicated to Slackware, if you need help specific to Linux Mint, like in your case, you are better off asking in the
dedicated forum.