replace NOTPARMDECL with TPARM_WORKAROUND

The old logic used a negative check to emit an extern declaration for
tparm(). This guarded against old platforms whose curses implementations
did not declare their own functions.

If there are still any platforms left that need this declaration, they
can set TPARM_WORKAROUND to get the old behavior back.

win/tty/termcap.c

@@ -895,8 +895,7 @@ cl_eos(void) /* free after Robert Viduya */
 
 #include <curses.h>
 
-#if !defined(LINUX) && !defined(__FreeBSD__) && !defined(__OpenBSD__) \
-	&& !defined(NOTPARMDECL)
+#if defined(TPARM_WORKAROUND)
 extern char *tparm();
 #endif