Add USB_FLASH_DRIVE_SUPPORT

Marlin/src/inc/MarlinConfigPre.h

@@ -21,6 +21,8 @@
  */
 #pragma once
 
+#define __MARLIN_FIRMWARE__
+
 //
 // Prefix header to acquire configurations
 //

Marlin/src/inc/SanityCheck.h

@@ -1830,4 +1830,8 @@ static_assert(COUNT(sanity_arr_3) <= XYZE_N, "DEFAULT_MAX_ACCELERATION has too m
   #error "PRINTCOUNTER requires EEPROM_SETTINGS. Please update your Configuration."
 #endif
 
+#if ENABLED(USB_FLASH_DRIVE_SUPPORT) && !(PIN_EXISTS(USB_CS) && PIN_EXISTS(USB_INTR))
+  #error "USB_CS_PIN and USB_INTR_PIN are required for USB_FLASH_DRIVE_SUPPORT."
+#endif
+
 #endif // _SANITYCHECK_H_