tree-wide: drop some misleading compiler warnings

gcc at some optimization levels thinks thes variables were used without
initialization. it's wrong, but let's make the message go anyway.

src/nspawn/nspawn.c

@@ -3830,7 +3830,7 @@ int main(int argc, char *argv[]) {
                 _cleanup_(sd_event_unrefp) sd_event *event = NULL;
                 _cleanup_(pty_forward_freep) PTYForward *forward = NULL;
                 _cleanup_(sd_netlink_unrefp) sd_netlink *rtnl = NULL;
-                ContainerStatus container_status;
+                ContainerStatus container_status = 0;
                 char last_char = 0;
                 int ifi = 0;
                 ssize_t l;

src/resolve/resolved-dns-packet.c

@@ -2143,7 +2143,7 @@ int dns_packet_extract(DnsPacket *p) {
 
                 for (i = 0; i < n; i++) {
                         _cleanup_(dns_resource_record_unrefp) DnsResourceRecord *rr = NULL;
-                        bool cache_flush;
+                        bool cache_flush = false;
 
                         r = dns_packet_read_rr(p, &rr, &cache_flush, NULL);
                         if (r < 0)