These functions are complicated because they need to be marked
"noreturn" for the compiler. There are several fundamentally
incompatible ways of doing that. Since we have only a few "noreturn"
functions, let's just list all of those in one header file of which
there is a completely different version for each compiler.
I planned to put just the file system routines into these files, but
there are starting to be so many of them that I don't want to
duplicate the same set for networking, subprocesses etc.
R7RS syntax is: (import (library name here))
We translate this into the internal path "library/name/here". This will allow
us to easily load libraries from files later on by appending the ".sld" file
name extension.