bpo-41756: Export PyGen_Send and wrap it in if-defs (#22677)

diff --git a/PC/python3dll.c b/PC/python3dll.c
index ff69ea7..153ba61 100644
--- a/PC/python3dll.c
+++ b/PC/python3dll.c
@@ -287,6 +287,7 @@
 EXPORT_FUNC(PyInterpreterState_New)
 EXPORT_FUNC(PyIter_Check)
 EXPORT_FUNC(PyIter_Next)
+EXPORT_FUNC(PyIter_Send)
 EXPORT_FUNC(PyList_Append)
 EXPORT_FUNC(PyList_AsTuple)
 EXPORT_FUNC(PyList_GetItem)