cc -O2 -pipe  -pthread  -Wall -Wextra -Werror -Wno-error=deprecated -Wno-error=deprecated-declarations signal/struct-sigevent.c -o signal/struct-sigevent -D_POSIX_C_SOURCE=202405L  -lm -lpthread 
signal/struct-sigevent.c:2:17: error: tentative definition has type 'struct sigevent' that is never completed
struct sigevent foo;
                ^
signal/struct-sigevent.c:2:8: note: forward declaration of 'struct sigevent'
struct sigevent foo;
       ^
1 error generated.