clang -O2  -Wall -Wextra -Werror=implicit-function-declaration unistd/setresuid.c -o unistd/setresuid -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE  -lm  -lintl
unistd/setresuid.c:11:7: error: implicit declaration of function 'getresuid' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
        if ( getresuid(&ruid, &euid, &suid) < 0 )
             ^
unistd/setresuid.c:11:7: note: did you mean 'geteuid'?
/usr/include/unistd.h:117:8: note: 'geteuid' declared here
uid_t    geteuid(void);
         ^
unistd/setresuid.c:13:7: error: implicit declaration of function 'setresuid' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
        if ( setresuid(ruid, euid, suid) < 0 )
             ^
unistd/setresuid.c:13:7: note: did you mean 'getresuid'?
unistd/setresuid.c:11:7: note: 'getresuid' declared here
        if ( getresuid(&ruid, &euid, &suid) < 0 )
             ^
2 errors generated.