Fix implicit declaration of functions tgetent() and tgetstr() in ./configure
leading otherwise to disabled terminal library support in gcal <= 4.1.

--- gcal-4.1/configure.ac
+++ gcal-4.1/configure.ac
@@ -319,7 +319,7 @@ if test "$gcal_cv_use_term" = yes; then
   AC_MSG_CHECKING(for working terminal libraries)
   SAVE_LIBS=$LIBS
   LIBS="$LIBS $TTYLIBS"
-  AC_TRY_LINK(,
+  AC_TRY_LINK([#include <term.h>],
     [tgetent(0); tgetflag(0); tgetnum(0); tgetstr(0);],
     [gcal_ttylibs_ok=yes])
   if test "$gcal_ttylibs_ok" = yes; then
@@ -334,7 +334,7 @@ if test "$gcal_cv_use_term" = yes; then
         [TTYLIBS="-ltermcap"])
       AC_MSG_CHECKING(for working terminal libraries again)
       LIBS="$LIBS $TTYLIBS"
-      AC_TRY_LINK(,
+      AC_TRY_LINK([#include <term.h>],
         [tgetent(0); tgetflag(0); tgetnum(0); tgetstr(0);],
         [gcal_ttylibs_ok=yes])
       if test "$gcal_ttylibs_ok" = yes; then
--- gcal-4.1/configure.ac   2025-06-29 15:24:25.000000000 +0200
+++ gcal-4.1/configure.ac   2025-06-29 15:29:46.000000000 +0200
@@ -320,7 +320,7 @@
   SAVE_LIBS=$LIBS
   LIBS="$LIBS $TTYLIBS"
   AC_TRY_LINK([#include <term.h>],
-    [tgetent(0); tgetflag(0); tgetnum(0); tgetstr(0);],
+    [tgetent(0,0); tgetflag(0); tgetnum(0); tgetstr(0,0);],
     [gcal_ttylibs_ok=yes])
   if test "$gcal_ttylibs_ok" = yes; then
     AC_DEFINE([HAVE_TTYLIBS], [1], [Link -lncurses or -ltermcap or -ltermlib 
to executable.])
@@ -335,7 +335,7 @@
       AC_MSG_CHECKING(for working terminal libraries again)
       LIBS="$LIBS $TTYLIBS"
       AC_TRY_LINK([#include <term.h>],
-        [tgetent(0); tgetflag(0); tgetnum(0); tgetstr(0);],
+        [tgetent(0,0); tgetflag(0); tgetnum(0); tgetstr(0,0);],
         [gcal_ttylibs_ok=yes])
       if test "$gcal_ttylibs_ok" = yes; then
         AC_DEFINE([HAVE_TTYLIBS], [1], [Link -lncurses or -ltermcap or 
-ltermlib to executable.])
@@ -352,7 +352,7 @@
         if test "$have_libtermlib" = yes; then
           AC_MSG_CHECKING(for working terminal libraries again)
           AC_TRY_LINK(,
-            [tgetent(0); tgetflag(0); tgetnum(0); tgetstr(0);],
+            [tgetent(0,0); tgetflag(0); tgetnum(0); tgetstr(0,0);],
             [gcal_libtermlib_ok=yes])
           if test "$gcal_libtermlib_ok" = yes; then
             AC_DEFINE([HAVE_TTYLIBS], [1], [Link -lncurses or -ltermcap or 
-ltermlib to executable.])
@@ -365,7 +365,7 @@
         TTYLIBS="-ltermlib"
         LIBS="$SAVE_LIBS $TTYLIBS"
         AC_TRY_LINK(,
-          [tgetent(0); tgetflag(0); tgetnum(0); tgetstr(0);],
+          [tgetent(0,0); tgetflag(0); tgetnum(0); tgetstr(0,0);],
           [gcal_libtermlib_ok=yes])
         if test "$gcal_libtermlib_ok" = yes; then
             AC_DEFINE([HAVE_TTYLIBS], [1], [Link -lncurses or -ltermcap or 
-ltermlib to executable.])