patch 8.2.1310: configure with Xcode 12 fails to check for tgetent

Problem:    Configure with Xcode 12 fails to check for tgetent.
Solution:   Declare tgetent(). (Ozaki Kiichi, closes #6558)

src/auto/configure

@@ -12106,7 +12106,7 @@ if test "x$olibs" = "x$LIBS"; then
 $as_echo_n "checking for tgetent()... " >&6; }
   cat confdefs.h - <<_ACEOF >conftest.$ac_ext
 /* end confdefs.h.  */
-
+int tgetent(char *, const char *);
 int
 main ()
 {

src/configure.ac

@@ -3510,7 +3510,7 @@ fi
 
 if test "x$olibs" = "x$LIBS"; then
   AC_MSG_CHECKING([for tgetent()])
-  AC_TRY_LINK([],
+  AC_TRY_LINK([int tgetent(char *, const char *);],
       [char s[10000]; int res = tgetent(s, "thisterminaldoesnotexist");],
 	AC_MSG_RESULT(yes),
 	AC_MSG_ERROR([NOT FOUND!

src/version.c

@@ -754,6 +754,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1310,
 /**/
     1309,
 /**/