cc -O2 -pipe  -pthread  -Wall -Wextra -Werror -Wno-error=deprecated -Wno-error=deprecated-declarations signal/SI_MESGQ.c -o signal/SI_MESGQ -D_POSIX_C_SOURCE=202405L  -lm -lpthread 
signal/SI_MESGQ.c:2:17: error: use of undeclared identifier 'SI_MESGQ'
int const foo = SI_MESGQ;
                ^
1 error generated.