cc -O2 -pipe -pthread  -Wall -Wextra -Werror -Wno-error=deprecated -Wno-error=deprecated-declarations sys_wait/union-sigval.c -o sys_wait/union-sigval -D_POSIX_C_SOURCE=202405L  -lm -lpthread -lrt  -lstdthreads -lcrypt
sys_wait/union-sigval.c:2:14: error: tentative definition has type 'union sigval' that is never completed
    2 | union sigval foo;
      |              ^
sys_wait/union-sigval.c:2:7: note: forward declaration of 'union sigval'
    2 | union sigval foo;
      |       ^
1 error generated.