variants/XMC1400: Add SPI pin definitions.

[ederjc]

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Description
This pull request includes changes to the pins_arduino.h files for the XMC1400_Arduino_Kit and XMC1400_XMC2GO variants. The changes involve adding external variable declarations for SPI pin assignments.

• variants/XMC1400/config/XMC1400_Arduino_Kit/pins_arduino.h: Added external variable declarations for SS, MOSI, MISO, and SCK to define SPI pin assignments.
• variants/XMC1400/config/XMC1400_XMC2GO/pins_arduino.h: Added external variable declarations for SS, MOSI, MISO, and SCK to define SPI pin assignments.

Related Issue
MHB and other libs using SPI not compiling on XMC1400-based boards.

[Copilot]

Copilot wasn't able to review any files in this pull request.

Files not reviewed (2)

• variants/XMC1400/config/XMC1400_Arduino_Kit/pins_arduino.h: Language not supported
• variants/XMC1400/config/XMC1400_XMC2GO/pins_arduino.h: Language not supported

[LinjingZhang]

Well, I didn't make this change before because I was not sure that using extern was the best way to do it. Refer to arduinoCore-AVR: https://github.com/arduino/ArduinoCore-avr/blob/master/variants/robot_control/pins_arduino.h#L62C1-L65C41
But if it's for a compile test pass - I don't see a problem with merge to master.