Safe changes from HAL cleanup

Marlin/src/HAL/shared/Marduino.h

@@ -31,6 +31,7 @@
 #undef sq             // Redefined by teensy3/wiring.h
 #undef SBI            // Redefined by arduino/const_functions.h
 #undef CBI            // Redefined by arduino/const_functions.h
+#undef UNUSED         // Redefined by stm32f4xx_hal_def.h
 
 #include <Arduino.h>  // NOTE: If included earlier then this line is a NOOP
 
@@ -74,3 +75,8 @@
 #ifndef M_PI
   #define M_PI 3.14159265358979323846f
 #endif
+
+// Remove compiler warning on an unused variable
+#ifndef UNUSED
+  #define UNUSED(x) ((void)(x))
+#endif