bpo-39273: Expose BUTTON5_* constants in the curses module if available (GH-17996)

diff --git a/Modules/_cursesmodule.c b/Modules/_cursesmodule.c
index 7175c72..7ab68c7 100644
--- a/Modules/_cursesmodule.c
+++ b/Modules/_cursesmodule.c
@@ -4870,6 +4870,14 @@ PyInit__curses(void)
     SetDictInt("BUTTON4_DOUBLE_CLICKED",   BUTTON4_DOUBLE_CLICKED);
     SetDictInt("BUTTON4_TRIPLE_CLICKED",   BUTTON4_TRIPLE_CLICKED);
 
+#if NCURSES_MOUSE_VERSION > 1
+    SetDictInt("BUTTON5_PRESSED",          BUTTON5_PRESSED);
+    SetDictInt("BUTTON5_RELEASED",         BUTTON5_RELEASED);
+    SetDictInt("BUTTON5_CLICKED",          BUTTON5_CLICKED);
+    SetDictInt("BUTTON5_DOUBLE_CLICKED",   BUTTON5_DOUBLE_CLICKED);
+    SetDictInt("BUTTON5_TRIPLE_CLICKED",   BUTTON5_TRIPLE_CLICKED);
+#endif
+
     SetDictInt("BUTTON_SHIFT",             BUTTON_SHIFT);
     SetDictInt("BUTTON_CTRL",              BUTTON_CTRL);
     SetDictInt("BUTTON_ALT",               BUTTON_ALT);