[patch] fix building C++ bindings in ncurses-5.4 with -fno-implicit-templates

[Mike Frysinger]

the C++ demo.cc fails to compile if you build with -fno-implicit-templates:
../obj_s/demo.o(.gnu.linkonce.t._ZN6MyMenuC1Ev+0x427): In function 
`MyMenu::MyMenu()':
: undefined reference to `vtable for NCursesUserItem<UserData>'
../obj_s/demo.o(.gnu.linkonce.t._ZN6MyMenuC1Ev+0x451): In function 
`MyMenu::MyMenu()':
: undefined reference to `vtable for MyAction<UserData>'

here's the two line fix:
--- c++/demo.cc
+++ c++/demo.cc
@@ -152,6 +152,8 @@
     return FALSE;
   }
 };
+template class MyAction<UserData>;
+template class NCURSES_IMPEXP NCursesUserItem<UserData>;
 
 class QuitItem : public NCursesMenuItem
 {
-mike