fix sign of strftime %z output with offsets <1 hour west of UTC

the sign character produced came from the sign of tm_gmtoff/3600 as an
integer division, which is zero for negative offsets smaller in
magnitude than 3600. instead of printing the hours and minutes as
separate fields, print them as a single value of the form
hours*100+minutes, which naturally has the correct sign.

src/time/strftime.c

@@ -181,9 +181,8 @@ const char *__strftime_fmt_1(char (*s)[100], size_t *l, int f, const struct tm *
 			*l = 0;
 			return "";
 		}
-		*l = snprintf(*s, sizeof *s, "%+.2ld%.2d",
-			(tm->__tm_gmtoff)/3600,
-			abs(tm->__tm_gmtoff%3600)/60);
+		*l = snprintf(*s, sizeof *s, "%+.4ld",
+			tm->__tm_gmtoff/3600*100 + tm->__tm_gmtoff%3600/60);
 		return *s;
 	case 'Z':
 		if (tm->tm_isdst < 0) {