Add tcsetpgrp_nobg() which acts like tcsetpgrp() but returns -1

for a background process.  This is safer than blocking SIGTTOU
which would cause tcsetpgrp() to succeed in the background.

src/sudo.h

@@ -271,4 +271,7 @@ int add_preserved_fd(struct preserved_fd_list *pfds, int fd);
 void closefrom_except(int startfd, struct preserved_fd_list *pfds);
 void parse_preserved_fds(struct preserved_fd_list *pfds, const char *fdstr);
 
+/* setpgrp_nobg.c */
+int tcsetpgrp_nobg(int fd, pid_t pgrp_id);
+
 #endif /* SUDO_SUDO_H */