musl: time-util: skip tm.tm_wday check

musl does not set tm_wday when it is explicitly requested.
The check is not necessary at all, it is just for safety.
Let's skip it when built with musl.

src/basic/time-util.c

@@ -889,7 +889,11 @@ static int parse_timestamp_impl(
                 if (!k || *k != ' ')
                         continue;
 
+#ifdef __GLIBC__
+                /* musl does not set tm_wday field and set 0 unless it is explicitly requested by %w or so.
+                 * In the below, let's only check tm_wday field only when built with glibc. */
                 weekday = day->nr;
+#endif
                 t = k + 1;
                 break;
         }