The compilation unit stores the directory from which qfcc was run and
any source files mentioned. This is similar to dwarf's compilation unit.
Right now, this is the only data in the new debug space, but more might
come in the future so it seems best to treat the debug space separately
in the object files.
It never really helped sort out the path issues when using build
directories. It worked well enough for single directory projects, but
things got messy very quickly, especially when mixing ruamoko libs with
external progs. A better method based on dwarf is coming.
Rather than prefixing free_ to the supplied name, suffix _freelist to the
supplied name. The biggest advantage of this is it allows the free-list to
be a structure member. It also cleans up the name-space a little.
Also move the ALLOC/FREE macros from qfcc.h to QF/alloc.h (needed to for
set.c).
Both modules are more generally useful than just for qfcc (eg, set
builtins for ruamoko).
