/opt/IBM/openxlC/17.1.1/bin/ibm-clang -pthread  -Wall -Wextra -Werror=implicit-function-declaration unistd/setresgid.c -o unistd/setresgid -D_GNU_SOURCE -D_BSD_SOURCE -D_ALL_SOURCE -D_DEFAULT_SOURCE -lm -lpthread -lrt -latomic
unistd/setresgid.c:11:7: error: call to undeclared function 'getresgid'; ISO C99 and later do not support implicit function declarations [-Werror,-Wimplicit-function-declaration]
        if ( getresgid(&rgid, &egid, &sgid) < 0 )
             ^
unistd/setresgid.c:13:7: error: call to undeclared function 'setresgid'; ISO C99 and later do not support implicit function declarations [-Werror,-Wimplicit-function-declaration]
        if ( setresgid(rgid, egid, sgid) < 0 )
             ^
2 errors generated.