[dfmc-conditions] with-simple-abort-retry-restart allows non-constant expressions

This is from my work in progress on restoring compilation passes.

This is required when the macro is used like:

````dylan
with-simple-abort-retry-restart
    (format-to-string("Abort %s and continue.", pass.name),
     format-to-string("Restart %s.", pass.name))
  ...
end;
````