Extend String to print 64-bit integers

[drws]

String(long long int) and String(unsigned long long int) are not defined for relevant platforms, so String() is unable to parse 64-bit integers. A minimal non-working example would be:

#include <Arduino.h>

void setup() {
  String(1LL); // String(1L) compiles
}

void loop() {
}

Which produces an error call of overloaded 'String(long long int)' is ambiguous.

[drws]

This has been solved lately in the arduino-esp32.