cc -pthread  -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 -lpthread  -liconv
unistd/setresuid.c:11:7: error: call to undeclared function 'getresuid'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
   11 |         if ( getresuid(&ruid, &euid, &suid) < 0 )
      |              ^
unistd/setresuid.c:13:7: error: call to undeclared function 'setresuid'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
   13 |         if ( setresuid(ruid, euid, suid) < 0 )
      |              ^
2 errors generated.