Hephaestus CMake Fix, master branch (2021.01.23.)

Made sure that the symbolic link creation during the build could for sure happen.

In a weird race condition (see: !39900 (comment 4109837)) the python output directory may not exist when the library was already built. Leading to a build error.

And while at it, I may as well have added a make_directory call for the library output directory. Even though that should really always exist by the time these commands are called...