Move code to suspend sudo when no pty is in use to separate file.

Use this in test_ptrace.c to be able to suspend just like sudo does.

src/sudo_exec.h

@@ -151,4 +151,7 @@ bool exec_ptrace_stopped(pid_t pid, int status, void *intercept);
 bool set_exec_filter(void);
 int exec_ptrace_seize(pid_t child);
 
+/* suspend_nopty.c */
+void suspend_sudo_nopty(int signo, pid_t ppgrp, pid_t cmnd_pid);
+
 #endif /* SUDO_EXEC_H */