Remove dead returns:

	return VAR/func(XX);
	return VAR;

The latter is never reached. Sent on tech-kern@, no disagreement.
Revert back to 1.7.
Document options COMPAT_70.
More tidyup after joerg's copy&paste disaster.  I have ddb symbols again.
PR/49087: Jarmo Jaakkola: Make sure that the first dependency is the C source
file so ${.IMPSRC} gets set correctly.