Supply prototypes where possible. This uncovered type errors with

thread entrypoints:
(lwpSelect, shutdown_sequence): Parameters didn't match thread entry
point prototype.
(lwpEntryPoint): Arguments didn't match thread entry point prototype.

Change linkage of functions without prototype declaration to static
where possible.

Remove some superflous declarations, replace others by suitable
includes.

src/lib/commands/bomb.c

@@ -214,7 +214,6 @@ bomb(void)
 static void
 pin_bomb(struct emp_qelem *list, struct sctstr *target)
 {
-    extern s_char *effadv();
     struct dchrstr *dcp;
     int nplanes;
     int nships;