Fixed led and reboot linker challenges in C++ environments

src/modules/systemlib/systemlib.c

@@ -50,6 +50,10 @@
 
 #include "systemlib.h"
 
+__EXPORT extern void systemreset(void) {
+	up_systemreset();
+}
+
 static void kill_task(FAR struct tcb_s *tcb, FAR void *arg);
 
 void killall()

src/modules/systemlib/systemlib.h

@@ -42,11 +42,11 @@
 #include <float.h>
 #include <stdint.h>
 
-/** Reboots the board */
-extern void up_systemreset(void) noreturn_function;
-
 __BEGIN_DECLS
 
+/** Reboots the board */
+__EXPORT void systemreset(void) noreturn_function;
+
 /** Sends SIGUSR1 to all processes */
 __EXPORT void killall(void);