test/formatc: improve 'inline' function handling

Apple seems to define some functions as `inline` but not `static` in
headers. The ghetto parser wasn't unbelievably happy with this.
test/formatc: improve standalone usage

Easier testing.
test/helpers: allow interning Pascal strings

os_system() returns a Pascal string, for example (it also NUL-terminates the
string, but that's neither here nor there).
TOCHANGE/os/shell: add tests

- The call to allocate_...() needs to go (and the ones to initialize logging
  hopefully as well). Blocked on #904.