Test fixes

    * Test initial carry logic in ADC immediate mode tests
    * Simplify decimal funneling tests in immediate mode
Enable illegal BCD break/debugging

    * Debugging builds will now segfault if an illegal BCD is encountered
    * Presumably current x86 undefined behavior does not 100% correspond to 6502
      undefined behavior ... (this bears further investigation)
Simplify ADC decimal mode test logic

    * Skip testing illegal BCDs
Simplify non-immediate mode tests

    * Removes testing decimal flag for these tests
Silence and fixes
SBC tests
ASL tests