Fix build on older (G)LIBC's w/o RB_SW_SUSPEND

Signed-off-by: Joachim Nilsson <troglobit@gmail.com>

reboot.c

@@ -29,6 +29,10 @@
 #include <unistd.h>
 #include <sys/reboot.h>
 
+#ifndef RB_SW_SUSPEND /* Since Linux 2.5.18, but not in GLIBC until 2.19 */
+#define RB_SW_SUSPEND	0xd000fce2
+#endif
+
 typedef enum {
 	CMD_UNKNOWN = -1,
 	CMD_REBOOT = 0,