#ifndef => #if !PIN_EXISTS

Marlin/src/HAL/HAL_STM32F1/HAL_spi_Stm32f1.cpp

  * @details Only configures SS pin since libmaple creates and initialize the SPI object
  */
 void spiBegin() {
-  #ifndef SS_PIN
+  #if !PIN_EXISTS(SS)
     #error "SS_PIN not defined!"
   #endif
   SET_OUTPUT(SS_PIN);

Marlin/src/HAL/HAL_TEENSY35_36/HAL_spi_Teensy.cpp

 // Standard SPI functions
 /** Initialise SPI bus */
 void spiBegin(void) {
-  #ifndef SS_PIN
+  #if !PIN_EXISTS(SS)
     #error SS_PIN not defined!
   #endif
   SET_OUTPUT(SS_PIN);
   SET_OUTPUT(MOSI_PIN);
 
   //#if DISABLED(SOFTWARE_SPI)
-  #if false
+  #if 0
     // set SS high - may be chip select for another SPI device
     #if SET_SPI_SS_HIGH
       WRITE(SS_PIN, HIGH);