clean up Arduino.h to avoid naming conflicts with stm32l4xx.h defines

Author: GrumpyOldPizza

cores/stm32l4/Arduino.h

@@ -82,6 +82,7 @@ enum BitOrder {
 
 #define ARM_MATH_CM4
 #include "stm32l4xx.h"
+#undef RTC
 #undef DAC1
 #undef SPI1
 #undef SPI2

libraries/RTC/src/RTC.cpp

@@ -28,7 +28,6 @@
 
 #include "Arduino.h"
 #include "stm32l4_wiring_private.h"
-#undef RTC
 #include "RTC.h"
 #include <time.h>
 

libraries/SPI/src/SPI.cpp

@@ -28,8 +28,6 @@
 
 #include "Arduino.h"
 #include "stm32l4_wiring_private.h"
-#undef SPI1
-#undef SPI2
 #include "SPI.h"
 
 /* The code below deserves some explanation. The SPIClass has really 2 modes of operation.