Unused variable ‘lockid’ on Solaris 11.4 in unix/socket.c

Building main on Solaris 11.4 I got the following warning:

unix/socket.c: In function ‘unwatch_fd’:
unix/socket.c:808:6: warning: unused variable ‘lockid’ [-Wunused-variable]
  int lockid = FDLOCK_ID(fd);
      ^~~~~~