fix const-correctness of argument to stime

it's unclear what the historical signature for this function was, but
semantically, the argument should be a pointer to const, and this is
what glibc uses. correct programs should not be using this function
anyway, so it's unlikely to matter.

src/linux/stime.c

@@ -2,7 +2,7 @@
 #include <time.h>
 #include <sys/time.h>
 
-int stime(time_t *t)
+int stime(const time_t *t)
 {
 	struct timeval tv = { .tv_sec = *t, .tv_usec = 0 };
 	return settimeofday(&tv, (void *)0);