Check the return value of the setgid and setuid functions

[YuGiOhJCJ]

Without checking the value of the setgid and setuid functions, an error happens while building:

$ ./Build
cc -I/usr/lib64/perl5/CORE -fPIC -g -Wall -Werror -pipe -Iserver -I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include -lglib-2.0 -c -D_REENTRANT -D_GNU_SOURCE -fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -D_FORTIFY_SOURCE=2 -O2 -fPIC -o server/fb-server.o server/fb-server.c
cc -I/usr/lib64/perl5/CORE -fPIC -g -Wall -Werror -pipe -Iserver -I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include -lglib-2.0 -c -D_REENTRANT -D_GNU_SOURCE -fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -D_FORTIFY_SOURCE=2 -O2 -fPIC -o server/log.o server/log.c
cc -I/usr/lib64/perl5/CORE -fPIC -g -Wall -Werror -pipe -Iserver -I/usr/include/glib-2.0 -I/usr/lib64/glib-2.0/include -lglib-2.0 -c -D_REENTRANT -D_GNU_SOURCE -fwrapv -fno-strict-aliasing -pipe -fstack-protector-strong -I/usr/local/include -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -D_FORTIFY_SOURCE=2 -O2 -fPIC -o server/tools.o server/tools.c
server/tools.c: In function ‘daemonize’:
server/tools.c:264:25: error: ignoring return value of ‘setgid’, declared with attribute warn_unused_result [-Werror=unused-result]
                         setgid(user->pw_gid);
                         ^
server/tools.c:265:25: error: ignoring return value of ‘setuid’, declared with attribute warn_unused_result [-Werror=unused-result]
                         setuid(user->pw_uid);
                         ^
cc1: all warnings being treated as errors
error building server/tools.o from 'server/tools.c' at /usr/share/perl5/ExtUtils/CBuilder/Base.pm line 173.

Moreover, it is a grave security error to omit checking for a failure return from the setuid function [1].

So, this is what I fixed.

Please accept my pull request.
Thank you.
Best regards.

ChangeLog:

• server/tools.c(daemonize): Modified file (check the return value of the setgid function).
• server/tools.c(daemonize): Modified file (check the return value of the setuid function).

[1] http://man7.org/linux/man-pages/man2/setuid.2.html