Move exec code to call into I/O log plugin to exec_iolog.c.

This will be shared with exec_nopty.c in the future to log
stdin/stdout/stderr without running the command in a pty.
Both exec_pty.c and exec_nopty.c now use the same closure.

src/sudo_intercept_common.c

@@ -51,8 +51,8 @@
 #include "sudo_compat.h"
 #include "sudo_conf.h"
 #include "sudo_debug.h"
-#include "sudo_fatal.h"
 #include "sudo_exec.h"
+#include "sudo_fatal.h"
 #include "sudo_gettext.h"
 #include "sudo_util.h"
 #include "intercept.pb-c.h"