Replacing intercepts - internal compartment utilities

[0152la]

After mulling over the system calls examples I worked in earlier today, I had a potential idea of how to integrate this idea better with the compartment implementation, while also getting rid of intercepts completely (including malloc intercepts).

We can introduce a new indirection layer, either as a library dependency, or perhaps as a header file with #defines, with implementations of DDC-bounded-safe functions. For instance, we would redirect printf calls to an internal printf implementation which has the same observable effect, but uses a write system call. We could also then move the malloc functions inside, which could use the DDC capability to know where to allocate space for the compartment they are in.

I'm unsure if this approach would be able to handle all libc functions, but I think I prefer it to having implicit transitions via the injections, and we would also simplify a lot of the code (particularly the ugly instruction building in comp_add_intercept.