Fix MKS_SGEN sanity check (#16501)

Marlin/src/pins/lpc1768/pins_MKS_SBASE.h

@@ -25,7 +25,9 @@
  * MKS SBASE pin assignments
  */
 
-#ifndef MCU_LPC1768
+#if defined(MKS_HAS_LPC1769) && !defined(MCU_LPC1769)
+  #error "Oops! Make sure you have the LPC1769 environment selected in your IDE."
+#elif !defined(MKS_HAS_LPC1769) && !defined(MCU_LPC1768)
   #error "Oops! Make sure you have the LPC1768 environment selected in your IDE."
 #endif
 

Marlin/src/pins/lpc1769/pins_MKS_SGEN.h

@@ -31,6 +31,7 @@
 
 #define BOARD_INFO_NAME   "MKS SGen"
 #define BOARD_WEBSITE_URL "github.com/makerbase-mks/MKS-SGEN"
+#define MKS_HAS_LPC1769
 
 #include "../lpc1768/pins_MKS_SBASE.h"