fix error code on time conversion overflows

POSIX mandates EOVERFLOW for this condition.

src/time/gmtime_r.c

@@ -5,7 +5,7 @@
 struct tm *__gmtime_r(const time_t *restrict t, struct tm *restrict tm)
 {
 	if (__secs_to_tm(*t, tm) < 0) {
-		errno = EINVAL;
+		errno = EOVERFLOW;
 		return 0;
 	}
 	tm->tm_isdst = 0;

src/time/localtime_r.c

@@ -6,7 +6,7 @@ struct tm *__localtime_r(const time_t *restrict t, struct tm *restrict tm)
 {
 	__secs_to_zone(*t, 0, &tm->tm_isdst, &tm->__tm_gmtoff, 0, &tm->__tm_zone);
 	if (__secs_to_tm((long long)*t - tm->__tm_gmtoff, tm) < 0) {
-		errno = EINVAL;
+		errno = EOVERFLOW;
 		return 0;
 	}
 	return tm;

src/time/mktime.c

@@ -25,6 +25,6 @@ time_t mktime(struct tm *tm)
 	return t;
 
 error:
-	errno = EINVAL;
+	errno = EOVERFLOW;
 	return -1;
 }

src/time/timegm.c

@@ -7,7 +7,7 @@ time_t timegm(struct tm *tm)
 	struct tm new;
 	long long t = __tm_to_secs(tm);
 	if (__secs_to_tm(t, &new) < 0) {
-		errno = EINVAL;
+		errno = EOVERFLOW;
 		return -1;
 	}
 	*tm = new;