*: fix fallout from -Wunused-parameter

function                                             old     new   delta
bbunpack                                             358     366      +8
passwd_main                                         1070    1072      +2
handle_incoming_and_exit                            2651    2653      +2
getpty                                                88      86      -2
script_main                                          975     972      -3
inetd_main                                          2036    2033      -3
dname_enc                                            377     373      -4
make_new_session                                     474     462     -12
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 3/5 up/down: 12/-24)            Total: -12 bytes
   text    data     bss     dec     hex filename
 797429     658    7428  805515   c4a8b busybox_old
 797417     658    7428  805503   c4a7f busybox_unstripped

diff --git a/networking/sendmail.c b/networking/sendmail.c
index 241028b..2eb01dc 100644
--- a/networking/sendmail.c
+++ b/networking/sendmail.c
@@ -551,11 +551,11 @@
 			int rc;
 
 			// retrieve message in ./tmp/
-			pop3_check(retr, (const char *)nmsg);
+			pop3_check(retr, (const char *)(ptrdiff_t)nmsg);
 			pop3_message(filename);
 			// delete message from server
 			if (opts & OPTF_z)
-				pop3_check("DELE %u", (const char*)nmsg);
+				pop3_check("DELE %u", (const char*)(ptrdiff_t)nmsg);
 
 			// run postprocessing program
 			if (*fargs) {