Missing implementations of ltoa, ultoa

[per1234]

Using:

• ArduinoCore-nRF528x-mbedos @ 7c86454
• ArduinoCore-API @ arduino/ArduinoCore-API@862fb23

As stated in ArduinoCore-API's itoa.h:
https://github.com/arduino/ArduinoCore-API/blob/namespace_arduino/api/itoa.h#L21-L23

// Standard C functions required in Arduino API
// If these functions are not provided by the standard library, the
// core should supply an implementation of them.

but this core does not provide implementations of ltoa and ultoa:

#include <api/itoa.h>

void setup() {
  char foo[3];
  ltoa(42, foo, 10);
  ultoa(42, foo, 10);
}

void loop() {}

C:\Users\per\AppData\Local\Temp\arduino_modified_sketch_625769/MissingConversions.ino:4: undefined reference to `ltoa'

C:\Users\per\AppData\Local\Temp\arduino_modified_sketch_625769/MissingConversions.ino:5: undefined reference to `ultoa'

This breaks the long and unsigned long overloads of the String class's constructor and concat:

void setup() {
  String bar1 = String((long)42);
  String bar2 = String((unsigned long)42);

  String foobar = "asdf";
  foobar.concat((long)42);
  foobar.concat((unsigned long)42);
}

void loop() {}

C:\Users\per\AppData\Local\Temp\arduino_build_659526/..\arduino_cache_182898\core\core_arduino_mbed_nano33ble_d56c57e38ae8cd7b62a9772ac9829484.a(String.cpp.o): In function `arduino::String::String(long, unsigned char)':

C:\Users\per\AppData\Local\Arduino15\packages\arduino\hardware\mbed\1.1.1\cores\arduino\api/String.cpp:100: undefined reference to `ltoa'

C:\Users\per\AppData\Local\Temp\arduino_build_659526/..\arduino_cache_182898\core\core_arduino_mbed_nano33ble_d56c57e38ae8cd7b62a9772ac9829484.a(String.cpp.o): In function `arduino::String::String(unsigned long, unsigned char)':

C:\Users\per\AppData\Local\Arduino15\packages\arduino\hardware\mbed\1.1.1\cores\arduino\api/String.cpp:108: undefined reference to `ultoa'

C:\Users\per\AppData\Local\Temp\arduino_build_659526/..\arduino_cache_182898\core\core_arduino_mbed_nano33ble_d56c57e38ae8cd7b62a9772ac9829484.a(String.cpp.o): In function `arduino::String::concat(long)':

C:\Users\per\AppData\Local\Arduino15\packages\arduino\hardware\mbed\1.1.1\cores\arduino\api/String.cpp:316: undefined reference to `ltoa'

C:\Users\per\AppData\Local\Temp\arduino_build_659526/..\arduino_cache_182898\core\core_arduino_mbed_nano33ble_d56c57e38ae8cd7b62a9772ac9829484.a(String.cpp.o): In function `arduino::String::concat(unsigned long)':

C:\Users\per\AppData\Local\Arduino15\packages\arduino\hardware\mbed\1.1.1\cores\arduino\api/String.cpp:323: undefined reference to `ultoa'

Reference:
https://forum.arduino.cc/index.php?topic=632997