Make suspend_parent.c out of lib/util and into src.

Nothing else uses it now.

src/sudo_exec.h

@@ -228,4 +228,7 @@ bool exec_ptrace_stopped(pid_t pid, int status, void *intercept);
 bool set_exec_filter(void);
 int exec_ptrace_seize(pid_t child);
 
+/* suspend_parent.c */
+void sudo_suspend_parent(int signo, pid_t my_pid, pid_t my_pgrp, pid_t cmnd_pid, void *closure, void (*callback)(void *, int));
+
 #endif /* SUDO_EXEC_H */