[CVS 980420] Still strength-reduce bug on HP-UX!

[Jim Wilson]

	You might want to return zero if get_condition returned zero or
	first_compare isn't the jump or the immediately preceeding
	real instruction.

The earlier get_condition_for_loop call would have returned zero if
get_condition returns zero, so there is no need to check for that
separately.

I'll add a check to verify that first_compare is prev_nonnote_insn (jump).
That does make the patch safer.  I was thinking that I could make the patch
work even if this wasn't true, but I didn't think it through very far, and it
doesn't seem like it is worth the extra effort.

Jim