Verständnisfrage AVR-GnuCC

#include <avr/io.h>

#include "init.h"

int main(void)

{

  init_system();

  return 0;

}

void init_system (void);

#include "init.h"

void init_system(void)

{

}

avr-gcc  -mmcu=atmega88 -Wall -gdwarf-2 -Os -std=gnu99 -funsigned-char -funsigned-bitfields -fpack-struct -fshort-enums -MD -MP -MT main.o -MF dep/main.o.d  -c  ../main.c

../main.c: In function 'main':

../main.c:6: warning: implicit declaration of function 'init_system'

avr-gcc -mmcu=atmega88 -Wl,-Map=MiGarden.map main.o init.o     -o MiGarden.elf

main.o: In function `main':

D:\Eigene Dateien\Projekte\MiGarden\MiGarden\default/../main.c:6: undefined reference to `init_system'

make: *** [MiGarden.elf] Error 1

Build failed with 1 errors and 1 warnings...