bpo-31919: Fix building the curses module on OpenIndiana. (GH-4211) (#4216)

(cherry picked from commit 894ebd065e02debf20c0657d26020ecc42b7534f)
diff --git a/Modules/_cursesmodule.c b/Modules/_cursesmodule.c
index 9149d76..75b1989 100644
--- a/Modules/_cursesmodule.c
+++ b/Modules/_cursesmodule.c
@@ -670,7 +670,7 @@
 #endif
 
 /* chgat, added by Fabian Kreutz <fabian.kreutz at gmx.net> */
-
+#ifdef HAVE_CURSES_WCHGAT
 static PyObject *
 PyCursesWindow_ChgAt(PyCursesWindowObject *self, PyObject *args)
 {
@@ -723,7 +723,7 @@
     }
     return PyCursesCheckERR(rtn, "chgat");
 }
-
+#endif
 
 static PyObject *
 PyCursesWindow_DelCh(PyCursesWindowObject *self, PyObject *args)
@@ -1569,7 +1569,9 @@
     {"attron",          (PyCFunction)PyCursesWindow_AttrOn, METH_VARARGS},
     {"attrset",         (PyCFunction)PyCursesWindow_AttrSet, METH_VARARGS},
     {"bkgd",            (PyCFunction)PyCursesWindow_Bkgd, METH_VARARGS},
+#ifdef HAVE_CURSES_WCHGAT
     {"chgat",           (PyCFunction)PyCursesWindow_ChgAt, METH_VARARGS},
+#endif
     {"bkgdset",         (PyCFunction)PyCursesWindow_BkgdSet, METH_VARARGS},
     {"border",          (PyCFunction)PyCursesWindow_Border, METH_VARARGS},
     {"box",             (PyCFunction)PyCursesWindow_Box, METH_VARARGS},