The problem was that we have to force SSA construction for memory values to
ensure the presence of the Phi[loop] nodes. Previously we did not do it
if we didn't introduce new values.

This fixes firm-testsuite/opt/jumpthreading8.c

This should really fix opt/fehler218.c oddities.

- This should fix some cases where we would not reassociate constants
  because of multiple users and missed address mode patterns for these
  cases.

This also allows to cleanup the finish neg/add carry flag fix code a
big.