clang -O2  -Wall -Wextra -Werror=implicit-function-declaration spawn/posix_spawnattr_getpgroup.c -o spawn/posix_spawnattr_getpgroup -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE  -lm  -lintl
spawn/posix_spawnattr_getpgroup.c:19:21: error: implicit declaration of function 'getpgid' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
        pid_t new_pgroup = getpgid(0);
                           ^
1 error generated.