samples/gettimeofday: Detect 32-bit timeval.tv_sec

Check to make sure the target is not using 32-bit time_t values which would
leave the application vulnerable to 2038 bugs.

Signed-off-by: Keith Packard <keithp@keithp.com>

samples/posix/gettimeofday/src/main.c

@@ -15,6 +15,12 @@ int main(void)
 {
 	struct timeval tv;
 
+	if (sizeof(tv.tv_sec) < sizeof(uint64_t)) {
+		printf("Error: sizeof(time_t) (%d) is less than 64 bits\n",
+		       (int) sizeof(tv.tv_sec));
+		return 1;
+	}
+
 	while (1) {
 		int res = gettimeofday(&tv, NULL);
 		time_t now = time(NULL);