oldland: fix one_cmplsi2 to use not rather than neg.

This is a bitwise inversion rather than integer negation.  Using neg
results in invalid code generation, and I found this manifesting as

	if (fun() != 0)
		return -1;
	return 0;

resulting in unconditionally returning -1;
oldland: add+sub clobber CC.

add, addc, sub and subc all clobber the carry flag, mark it as such to
avoid cmp, add, beq type sequences from resulting in incorrect branches.