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/mfir.c

@@ -780,7 +780,6 @@ quiet_bigdef(int attacker, struct emp_qelem *list, natid own, natid aown,
     struct sctstr firing;
     struct nstr_sect ns;
     struct flist *fp;
-    double techfact(int, double);
     extern int torpedo_damage;
     int gun;