Clean up pins self-checks

Marlin/src/pins/mega/pins_MEGACONTROLLER.h

 
 #ifndef __AVR_ATmega2560__
   #error "Oops! Select 'Arduino/Genuino Mega or Mega 2560' in 'Tools > Board.'"
-#endif
-
-#if HOTENDS > 2 || E_STEPPERS > 2
+#elif HOTENDS > 2 || E_STEPPERS > 2
   #error "Mega Controller supports up to 2 hotends / E-steppers. Comment out this line to continue."
 #endif
 

Marlin/src/pins/mega/pins_MINITRONICS.h

 
 #ifndef __AVR_ATmega1281__
   #error "Oops! Select 'Minitronics' in 'Tools > Board.'"
-#endif
-
-#if HOTENDS > 2 || E_STEPPERS > 2
+#elif HOTENDS > 2 || E_STEPPERS > 2
   #error "Minitronics supports up to 2 hotends / E-steppers. Comment out this line to continue."
 #endif
 

Marlin/src/pins/ramps/pins_AZTEEG_X3.h

 
 #ifndef __AVR_ATmega2560__
   #error "Oops! Select 'Arduino/Genuino Mega or Mega 2560' in 'Tools > Board.'"
-#endif
-
-#if HOTENDS > 2 || E_STEPPERS > 2
+#elif HOTENDS > 2 || E_STEPPERS > 2
   #error "Azteeg X3 supports up to 2 hotends / E-steppers. Comment out this line to continue."
 #endif
 

Marlin/src/pins/ramps/pins_AZTEEG_X3_PRO.h

 
 #ifndef __AVR_ATmega2560__
   #error "Oops! Select 'Arduino/Genuino Mega or Mega 2560' in 'Tools > Board.'"
-#endif
-
-#if HOTENDS > 5 || E_STEPPERS > 5
+#elif HOTENDS > 5 || E_STEPPERS > 5
   #error "Azteeg X3 Pro supports up to 5 hotends / E-steppers. Comment out this line to continue."
 #endif
 

Marlin/src/pins/ramps/pins_FORMBOT_RAPTOR.h

 
 #ifndef __AVR_ATmega2560__
   #error "Oops! Select 'Arduino/Genuino Mega or Mega 2560' in 'Tools > Board.'"
-#endif
-
-#if HOTENDS > 3 || E_STEPPERS > 3
+#elif HOTENDS > 3 || E_STEPPERS > 3
   #error "Formbot supports up to 3 hotends / E-steppers. Comment out this line to continue."
 #endif
 

Marlin/src/pins/ramps/pins_FORMBOT_TREX2PLUS.h

 
 #ifndef __AVR_ATmega2560__
   #error "Oops! Select 'Arduino/Genuino Mega or Mega 2560' in 'Tools > Board.'"
-#endif
-
-#if HOTENDS > 2 || E_STEPPERS > 2
+#elif HOTENDS > 2 || E_STEPPERS > 2
   #error "Formbot supports up to 2 hotends / E-steppers. Comment out this line to continue."
 #endif
 

Marlin/src/pins/ramps/pins_FORMBOT_TREX3.h

 
 #ifndef __AVR_ATmega2560__
   #error "Oops! Select 'Arduino/Genuino Mega or Mega 2560' in 'Tools > Board.'"
-#endif
-
-#if HOTENDS > 2 || E_STEPPERS > 2
+#elif HOTENDS > 2 || E_STEPPERS > 2
   #error "Formbot supports up to 2 hotends / E-steppers. Comment out this line to continue."
 #endif
 

Marlin/src/pins/ramps/pins_RUMBA.h

 
 #ifndef __AVR_ATmega2560__
   #error "Oops! Select 'Arduino/Genuino Mega or Mega 2560' in 'Tools > Board.'"
-#endif
-
-#if HOTENDS > 3 || E_STEPPERS > 3
+#elif HOTENDS > 3 || E_STEPPERS > 3
   #error "RUMBA supports up to 3 hotends / E-steppers. Comment out this line to continue."
 #endif
 

Marlin/src/pins/ramps/pins_TRONXY_V3_1_0.h

 
 #ifndef __AVR_ATmega2560__
   #error "Oops! Select 'Arduino/Genuino Mega or Mega 2560' in 'Tools > Board.'"
-#endif
-
-#if HOTENDS > 2 || E_STEPPERS > 2
+#elif HOTENDS > 2 || E_STEPPERS > 2
   #error "TRONXY-V3-1.0 supports only 2 hotends/E-steppers. Comment out this line to continue."
 #endif
 

Marlin/src/pins/ramps/pins_Z_BOLT_X_SERIES.h

  *  Z-Bolt X Series board – based on Arduino Mega2560
  */
 
-#if HOTENDS > 4 || E_STEPPERS > 4
-  #error "Z-Bolt X Series board supports up to 4 hotends / E-steppers."
-#endif
-
 #if !defined(__AVR_ATmega2560__)
   #error "Oops! Select 'Arduino/Genuino Mega or Mega 2560' in 'Tools > Board.'"
+#elif HOTENDS > 4 || E_STEPPERS > 4
+  #error "Z-Bolt X Series board supports up to 4 hotends / E-steppers."
 #endif
 
 #define BOARD_NAME "Z-Bolt X Series"

Marlin/src/pins/stm32/pins_ARMED.h

 
 #ifndef STM32F4
   #error "Oops! Select an STM32F4 board in 'Tools > Board.'"
+#elif HOTENDS > 2 || E_STEPPERS > 2
+  #error "Arm'ed supports up to 2 hotends / E-steppers."
 #endif
 
 #ifndef ARMED_V1_0
 #undef E2END // Defined in Arduino Core STM32 to be used with EEPROM emulation. This board uses a real EEPROM.
 #define E2END 0xFFF // 4KB
 
-#if HOTENDS > 2 || E_STEPPERS > 2
-  #error "Arm'ed supports up to 2 hotends / E-steppers."
-#endif
-
 //
 // Limit Switches
 //

Marlin/src/pins/stm32/pins_BIGTREE_SKR_PRO_V1.1.h

 
 #ifndef TARGET_STM32F4
   #error "Oops! Select an STM32F4 board in 'Tools > Board.'"
-#endif
-
-#if HOTENDS > 3 || E_STEPPERS > 3
+#elif HOTENDS > 3 || E_STEPPERS > 3
   #error "BIGTREE SKR Pro V1.1 supports up to 3 hotends / E-steppers."
 #endif
 

Marlin/src/pins/stm32/pins_BLACK_STM32F407VE.h

 
 #if !defined(STM32F4) && !defined(STM32F4xx)
   #error "Oops! Select an STM32F4 board in 'Tools > Board.'"
+#elif HOTENDS > 2 || E_STEPPERS > 2
+  #error "Black STM32F4VET6 supports up to 2 hotends / E-steppers."
 #endif
 
 #ifndef BOARD_NAME
 //#define E2END 0x1FFF // 8KB
 #define SRAM_EEPROM_EMULATION
 
-#if HOTENDS > 2 || E_STEPPERS > 2
-  #error "Black STM32F4VET6 supports up to 2 hotends / E-steppers."
-#endif
-
 //
 // Servos
 //

Marlin/src/pins/stm32/pins_MKS_ROBIN.h

 
 #ifndef __STM32F1__
   #error "Oops! Select an STM32F1 board in 'Tools > Board.'"
-#endif
-
-#if HOTENDS > 2 || E_STEPPERS > 2
+#elif HOTENDS > 2 || E_STEPPERS > 2
   #error "MKS Robin supports up to 2 hotends / E-steppers. Comment out this line to continue."
 #endif
 

Marlin/src/pins/stm32/pins_MKS_ROBIN_MINI.h

 
 #ifndef __STM32F1__
   #error "Oops! Select an STM32F1 board in 'Tools > Board.'"
-#endif
-
-#if HOTENDS > 1 || E_STEPPERS > 1
+#elif HOTENDS > 1 || E_STEPPERS > 1
   #error "MKS Robin mini supports up to 1 hotends / E-steppers. Comment out this line to continue."
 #endif
 

Marlin/src/pins/stm32/pins_MKS_ROBIN_NANO.h

 
 #ifndef __STM32F1__
   #error "Oops! Select an STM32F1 board in 'Tools > Board.'"
-#endif
-
-#if HOTENDS > 2 || E_STEPPERS > 2
+#elif HOTENDS > 2 || E_STEPPERS > 2
   #error "MKS Robin nano supports up to 2 hotends / E-steppers. Comment out this line to continue."
 #endif
 

Marlin/src/pins/stm32/pins_RUMBA32.h

 
 #ifndef STM32F4
   #error "Oops! Select an STM32F4 board in 'Tools > Board.'"
+#elif HOTENDS > 3 || E_STEPPERS > 3
+  #error "RUMBA32 supports up to 3 hotends / E-steppers."
 #endif
 
 #define RUMBA32_V1_0
 //#define I2C_EEPROM
 #define E2END 0xFFF // 4KB
 
-#if HOTENDS > 3 || E_STEPPERS > 3
-  #error "RUMBA32 supports up to 3 hotends / E-steppers."
-#endif
-
 //
 // Limit Switches
 //

Marlin/src/pins/stm32/pins_STM32F4.h

 
 #if !defined(STM32F4) && !defined(STM32F4xx)
   #error "Oops! Select an STM32F4 board in 'Tools > Board.'"
+#elif HOTENDS > 2 || E_STEPPERS > 2
+  #error "STM32F4 supports up to 2 hotends / E-steppers."
 #endif
 
 #define BOARD_NAME           "Misc. STM32F4"
 // Ignore temp readings during development.
 //#define BOGUS_TEMPERATURE_GRACE_PERIOD 2000
 
-#if HOTENDS > 2 || E_STEPPERS > 2
-  #error "STM32F4 supports up to 2 hotends / E-steppers."
-#endif
-
 //
 // Limit Switches
 //

Marlin/src/pins/stm32/pins_THE_BORG.h

 
 #if !defined(STM32F7)
   #error "Oops! Select an STM32F7 board in 'Tools > Board.'"
+#elif HOTENDS > 3 || E_STEPPERS > 3
+  #error "The-Borg supports up to 3 hotends / E-steppers."
 #endif
 
 #define BOARD_NAME           "The-Borge"
 // Ignore temp readings during development.
 //#define BOGUS_TEMPERATURE_GRACE_PERIOD 2000
 
-#if HOTENDS > 3 || E_STEPPERS > 3
-  #error "The-Borg supports up to 3 hotends / E-steppers."
-#endif
-
 //
 // Limit Switches
 //