Fix c++17 warning

src/SigLed.cpp

@@ -32,7 +32,7 @@ void SigLED::rtLed()
             _state = LS_RUN;
             ++_ptr;
             ++_pptr;
-            // no break - we fall through LS_RUN state
+            [[fallthrough]]; // no break - we fall through LS_RUN state
 
         case LS_RUN: {
             uint8_t instr = getInstruction();