Add missing prototype for _termios_setup() - causing build warnings

src/xpdev/conwrap.h

-/* conwrap.h */
-
 /* Cross-platform local console I/O wrapppers */
 
-/* $Id: conwrap.h,v 1.6 2018/07/24 01:13:09 rswindell Exp $ */
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@@ -17,21 +13,9 @@
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@@ -40,6 +24,7 @@
 
 #if defined(__unix__)
 
+    void _termios_setup(void);
     void _termios_reset(void);
     void _echo_on(void);
     void _echo_off(void);