Fix comparisons (aka usage of flag/CCR register)

m68k/aasmcpu.pas, taicpu.spilling_get_operation_type:
  * add all Sxx instructions as "operand_write" instructions

m68k/n68kadd.pas, t68kaddnode.getresflags:
  * use the correct operation in case of swapped nodes

m68k/cgcpu.pas, tcg68k.g_flags2reg:
  - don't move a 0 to the register, because this will CLR it and thus the flags won't be valid anymore...
  - NEG would have been the wrong operation (NOT would have been correct), but it isn't needed anyway...
  * simplify the method by handling the address register case only when necessary



git-svn-id: http://svn.freepascal.org/svn/fpc/trunk@23383 3ad0048d-3df7-0310-abae-a5850022a9f2