cc -O2 -pipe  -pthread  -Wall -Wextra -Werror -Wno-error=deprecated -Wno-error=deprecated-declarations pthread/PTHREAD_NULL.c -o pthread/PTHREAD_NULL -D_POSIX_C_SOURCE=202405L  -lm -lpthread 
pthread/PTHREAD_NULL.c:2:24: error: use of undeclared identifier 'PTHREAD_NULL'
pthread_t  const foo = PTHREAD_NULL;
                       ^
1 error generated.