The standard library comes as a collection of public repositories on github/SacBase.
In the case of the source code, you'll have to check out the latest versions of the the
stdlib repository and possibly further repositories from
SacBase, you need to build and install the standard library.
Normally, the install of the stdlib should work fine in which case may want to proceed to the
If you are curious about the details on where the built modules are actually stored or on how platform dependent versions are created and kept apart you can read up about cross compilation and the SBI (SaC Binary Interface).