cpu/atmega2560/startup.c: Add __attribute__((used)) to init functions

cpu/atmega2560/startup.c

@@ -43,19 +43,20 @@ extern void __libc_init_array(void);
  * which should never be reached but just in case jumps to exit.
  * This way there should be no way to call main directly.
  */
-void init7_ovr(void) __attribute__((naked)) __attribute__((section(".init7")));
-void init8_ovr(void) __attribute__((naked)) __attribute__((section(".init8")));
+void init7_ovr(void) __attribute__((section(".init7")));
+void init8_ovr(void) __attribute__((section(".init8")));
 
 
-void init7_ovr(void)
+__attribute__((used,naked)) void init7_ovr(void)
 {
     __asm__("call reset_handler");
 }
 
-void init8_ovr(void)
+__attribute__((used,naked)) void init8_ovr(void)
 {
     __asm__("jmp exit");
 }
+
 /**
  * @brief This function is the entry point after a system reset
  *
@@ -63,7 +64,7 @@ void init8_ovr(void)
  * 1. initialize the board (sync clock, setup std-IO)
  * 2. initialize and start RIOTs kernel
  */
-void reset_handler(void)
+__attribute__((used)) void reset_handler(void)
 {
     /* initialize the board and startup the kernel */
     board_init();