Extend the NOT+ADC-trick (sic) for SUB to SBB.

Extend the NOT+ADC-trick (sic) for SUB to SBB.

This should fix 403.gcc.
A SBB with AM could not fulfill its should_be_same contraint, so the AM gets split from the SBB.
The Load of the AM gets assigned the out register of the SBB, which violates the !in_r5 constraint of the SBB.
Therefore it's necessary to turn the SBB into NOT+ADC.