clang -O2  -Wall -Wextra -Werror=implicit-function-declaration sys_wait/waitid.c -o sys_wait/waitid -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE  -lm  -lintl
sys_wait/waitid.c:36:7: error: implicit declaration of function 'waitid' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
        if ( waitid(P_PID, children[0], &info, 0) < 0 )
             ^
sys_wait/waitid.c:36:7: note: did you mean 'waitpid'?
/usr/include/sys/wait.h:176:7: note: 'waitpid' declared here
pid_t   waitpid(pid_t, int *, int);
        ^
sys_wait/waitid.c:36:14: error: use of undeclared identifier 'P_PID'
        if ( waitid(P_PID, children[0], &info, 0) < 0 )
                    ^
sys_wait/waitid.c:50:22: error: implicit declaration of function 'getpgid' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
        if ( waitid(P_PGID, getpgid(0), &info, 0) < 0 )
                            ^
sys_wait/waitid.c:50:14: error: use of undeclared identifier 'P_PGID'
        if ( waitid(P_PGID, getpgid(0), &info, 0) < 0 )
                    ^
sys_wait/waitid.c:62:14: error: use of undeclared identifier 'P_PGID'
        if ( waitid(P_PGID, children[2], &info, 0) < 0 )
                    ^
sys_wait/waitid.c:74:14: error: use of undeclared identifier 'P_ALL'
        if ( waitid(P_ALL, 0, &info, 0) < 0 )
                    ^
sys_wait/waitid.c:86:14: error: use of undeclared identifier 'P_ALL'
        if ( waitid(P_ALL, 0, &info, 0) < 0 )
                    ^
7 errors generated.