LibCore: Add syscall wrapper for getgrnam()

Author: https://github.com/kennethmyhra
Commit: c4bd46023b
Pull-request: https://github.com/SerenityOS/serenity/pull/11101
Reviewed-by: https://github.com/awesomekling
Reviewed-by: https://github.com/bgianfo ✅
Reviewed-by: https://github.com/creator1creeper1 ✅
Reviewed-by: https://github.com/kleinesfilmroellchen ✅

Userland/Libraries/LibCore/System.h

@@ -8,6 +8,7 @@
 #pragma once
 
 #include <AK/Error.h>
+#include <grp.h>
 #include <pwd.h>
 #include <signal.h>
 #include <sys/stat.h>
@@ -47,5 +48,6 @@ ErrorOr<void> tcsetattr(int fd, int optional_actions, struct termios const&);
 ErrorOr<void> chmod(StringView pathname, mode_t mode);
 ErrorOr<void> chown(StringView pathname, uid_t uid, gid_t gid);
 ErrorOr<struct passwd> getpwnam(StringView name);
+ErrorOr<struct group> getgrnam(StringView name);
 
 }