Set preprocessor defines for various boards in `default.yaml`

[ianfixes]

This looks like a good resource for what #defines might be available

https://arduino.stackexchange.com/questions/21137/arduino-how-to-get-the-board-type-in-code

#if defined(TEENSYDUINO) 

    //  --------------- Teensy -----------------

    #if defined(__AVR_ATmega32U4__)
        #define BOARD "Teensy 2.0"
    #elif defined(__AVR_AT90USB1286__)       
        #define BOARD "Teensy++ 2.0"
    #elif defined(__MK20DX128__)       
        #define BOARD "Teensy 3.0"
    #elif defined(__MK20DX256__)       
        #define BOARD "Teensy 3.2" // and Teensy 3.1 (obsolete)
    #elif defined(__MKL26Z64__)       
        #define BOARD "Teensy LC"
    #elif defined(__MK64FX512__)
        #define BOARD "Teensy 3.5"
    #elif defined(__MK66FX1M0__)
        #define BOARD "Teensy 3.6"
    #else
       #error "Unknown board"
    #endif

#else // --------------- Arduino ------------------

    #if   defined(ARDUINO_AVR_ADK)       
        #define BOARD "Mega Adk"
    #elif defined(ARDUINO_AVR_BT)    // Bluetooth
        #define BOARD "Bt"
    #elif defined(ARDUINO_AVR_DUEMILANOVE)       
        #define BOARD "Duemilanove"
    #elif defined(ARDUINO_AVR_ESPLORA)       
        #define BOARD "Esplora"
    #elif defined(ARDUINO_AVR_ETHERNET)       
        #define BOARD "Ethernet"
    #elif defined(ARDUINO_AVR_FIO)       
        #define BOARD "Fio"
    #elif defined(ARDUINO_AVR_GEMMA)
        #define BOARD "Gemma"
    #elif defined(ARDUINO_AVR_LEONARDO)       
        #define BOARD "Leonardo"
    #elif defined(ARDUINO_AVR_LILYPAD)
        #define BOARD "Lilypad"
    #elif defined(ARDUINO_AVR_LILYPAD_USB)
        #define BOARD "Lilypad Usb"
    #elif defined(ARDUINO_AVR_MEGA)       
        #define BOARD "Mega"
    #elif defined(ARDUINO_AVR_MEGA2560)       
        #define BOARD "Mega 2560"
    #elif defined(ARDUINO_AVR_MICRO)       
        #define BOARD "Micro"
    #elif defined(ARDUINO_AVR_MINI)       
        #define BOARD "Mini"
    #elif defined(ARDUINO_AVR_NANO)       
        #define BOARD "Nano"
    #elif defined(ARDUINO_AVR_NG)       
        #define BOARD "NG"
    #elif defined(ARDUINO_AVR_PRO)       
        #define BOARD "Pro"
    #elif defined(ARDUINO_AVR_ROBOT_CONTROL)       
        #define BOARD "Robot Ctrl"
    #elif defined(ARDUINO_AVR_ROBOT_MOTOR)       
        #define BOARD "Robot Motor"
    #elif defined(ARDUINO_AVR_UNO)       
        #define BOARD "Uno"
    #elif defined(ARDUINO_AVR_YUN)       
        #define BOARD "Yun"

    // These boards must be installed separately:
    #elif defined(ARDUINO_SAM_DUE)       
        #define BOARD "Due"
    #elif defined(ARDUINO_SAMD_ZERO)       
        #define BOARD "Zero"
    #elif defined(ARDUINO_ARC32_TOOLS)       
        #define BOARD "101"
    #else
       #error "Unknown board"
    #endif

#endif

[ianfixes]

Merging with #89