Add new utility and init script swclock that sets the system time based on

the mtime of a file. It saves the shutdown time to this file also.
This is handy for systems without a working RTC chip.
Based on an idea by Michael A. Smith <michael@smith-li.com>.
Fixes Gentoo #272073.

src/includes/rc-misc.h

@@ -35,6 +35,7 @@
 #include <sys/stat.h>
 #include <errno.h>
 #include <stdbool.h>
+#include <stdlib.h>
 #include <string.h>
 
 #define RC_LEVEL_BOOT           "boot"