Skip impossible PWM sanity-checks

Marlin/src/HAL/STM32F1/HAL.h

@@ -160,6 +160,7 @@ void HAL_idletask();
 
 #ifndef digitalPinHasPWM
   #define digitalPinHasPWM(P) (PIN_MAP[P].timer_device != nullptr)
+  #define NO_COMPILE_TIME_PWM
 #endif
 
 #define CRITICAL_SECTION_START()  uint32_t primask = __get_primask(); (void)__iCliRetVal()

Marlin/src/inc/SanityCheck.h

@@ -1985,7 +1985,7 @@ static_assert(Y_MAX_LENGTH >= Y_BED_SIZE, "Movement bounds (Y_MIN_POS, Y_MAX_POS
 /**
  * Auto Fan check for PWM pins
  */
-#if HAS_AUTO_FAN && EXTRUDER_AUTO_FAN_SPEED != 255
+#if HAS_AUTO_FAN && EXTRUDER_AUTO_FAN_SPEED != 255 && DISABLED(NO_COMPILE_TIME_PWM)
   #define AF_ERR_SUFF "_AUTO_FAN_PIN is not a PWM pin. Set EXTRUDER_AUTO_FAN_SPEED to 255."
   #if HAS_AUTO_FAN_0
     static_assert(PWM_PIN(E0_AUTO_FAN_PIN), "E0" AF_ERR_SUFF);