init,halt: portability improvements

* make init and halt use the same RB_* constants for reboot()
* conditionalize the Linux-specific code

Inspired by init.init.diff from the Debian kFreeBSD patches at:
http://svn.debian.org/viewsvn/d-i/people/slackydeb/kfreebsd/busybox/1.14/debian

Signed-off-by: Jeremie Koenig <jk@jk.fr.eu.org>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

init/halt.c

@@ -8,7 +8,7 @@
  */
 
 #include "libbb.h"
-#include <sys/reboot.h>
+#include "reboot.h"
 
 #if ENABLE_FEATURE_WTMP
 #include <sys/utsname.h>
@@ -36,18 +36,6 @@ static void write_wtmp(void)
 #define write_wtmp() ((void)0)
 #endif
 
-#ifndef RB_HALT_SYSTEM
-#define RB_HALT_SYSTEM RB_HALT
-#endif
-
-#ifndef RB_POWERDOWN
-/* Stop system and switch power off if possible.  */
-# define RB_POWERDOWN   0x4321fedc
-#endif
-#ifndef RB_POWER_OFF
-# define RB_POWER_OFF RB_POWERDOWN
-#endif
-
 
 int halt_main(int argc, char **argv) MAIN_EXTERNALLY_VISIBLE;
 int halt_main(int argc UNUSED_PARAM, char **argv)