Printf not working with megaAVR - fix

[Cobalt6700]

Hi,

I have been playing around with Arduino Nano Every's using the Arduino megaAVR Baords Library.
I needed to debug and found radio.printDetails(); was not outputting to serial monitor.
Tried with the example code GettingStarted to confirm it was not my code that was causing the issue. Switched Registers Emulation to ATMEGA328 with no change. Swapping out with a 328P Nano worked fine.

Not sure if this is the correct way of doing it, however after a bit of research and testing, the below "if defined" additions to printf.h seem to solve the issue.

#if defined (ARDUINO_ARCH_AVR) || defined (__ARDUINO_X86__) || defined (ARDUINO_ARCH_MEGAAVR)

int serial_putc(char c, FILE *)
{
    Serial.write(c);
    return c;
}

#elif defined (ARDUINO_ARCH_MBED)
REDIRECT_STDOUT_TO(Serial);

#endif // defined (ARDUINO_ARCH_AVR) || defined (__ARDUINO_X86__) || defined (ARDUINO_ARCH_MBED) || defined (ARDUINO_ARCH_MEGAAVR)

void printf_begin(void)
{
    #if defined (ARDUINO_ARCH_AVR) || defined (ARDUINO_ARCH_MEGAAVR)
    fdevopen(&serial_putc, 0);

    #elif defined (__ARDUINO_X86__)
    // For redirect stdout to /dev/ttyGS0 (Serial Monitor port)
    stdout = freopen("/dev/ttyGS0", "w", stdout);
    delay(500);
    printf("Redirecting to Serial...");
    #endif // defined(__ARDUINO_X86__)
}

[2bndy5]

I have no objections to this. A simple PR for this is welcome.

[Cobalt6700]

Magic, PR open.