tree-wide: avoid uninitialized warning on _cleanup_ variables

With some versions of the compiler, the _cleanup_ attr makes it think
the variable might be freed/closed when uninitialized, even though it
cannot happen. The added cost is small enough to be worth the benefit,
and optimized builds will help reduce it even further.

src/basic/time-util.c

@@ -1547,7 +1547,7 @@ int time_change_fd(void) {
                 .it_value.tv_sec = TIME_T_MAX,
         };
 
-        _cleanup_close_ int fd;
+        _cleanup_close_ int fd = -1;
 
         assert_cc(sizeof(time_t) == sizeof(TIME_T_MAX));