Adding checks for fd omission

Adding function check_fds to new file fd.c. The function check_fds
should be called in every setuid/setgid program.

Co-developed-by: Alejandro Colomar <alx@kernel.org>

src/newgrp.c

@@ -390,6 +390,9 @@ int main (int argc, char **argv)
 #ifdef WITH_AUDIT
 	audit_help_open ();
 #endif
+
+	check_fds ();
+
 	(void) setlocale (LC_ALL, "");
 	(void) bindtextdomain (PACKAGE, LOCALEDIR);
 	(void) textdomain (PACKAGE);