The reason the sketch compiles in 1.0.5 and not on the 1.5.3 (designed for Intel Galileo) is because the AVR addresses registers referred to on 1.0.5 are for the atmel chip used in Arduino.
In addition to what Intel_JEspinoza has said, here're the details on that function: http://www.nongnu.org/avr-libc/user-manual/group__avr__stdlib.html#ga060c998e77fb5fc0d3168b3ce8771d42
You can simply write your own function, which will do the needful (don't forget to remove that .h include after that).
As far as uncle Google suggests, folks in the Arduino forum here: 'dtostrf' was not declared in this scope - Arduino Forum
have already come up with the solution, it's referenced in that thread, here's the direct link, I haven't tried it myself, but it looks UNIX-enough at first glance, so try it out: https://github.com/arduino/Arduino/blob/a2e7413d229812ff123cb8864747558b270498f1/hardware/arduino/sam/cores/arduino/avr/dtostrf.c