Issue #13959: Re-implement imp.get_suffixes() in Lib/imp.py.

This introduces a new function, imp.extension_suffixes(), which is
currently undocumented. That is forthcoming once issue #14657 is
resolved and how to expose file suffixes is decided.
diff --git a/Python/dynload_win.c b/Python/dynload_win.c
index 7bf3dfc..9c48a2d 100644
--- a/Python/dynload_win.c
+++ b/Python/dynload_win.c
@@ -15,13 +15,13 @@
 extern ULONG_PTR _Py_ActivateActCtx();
 void _Py_DeactivateActCtx(ULONG_PTR cookie);
 
-const struct filedescr _PyImport_DynLoadFiletab[] = {
+const char *_PyImport_DynLoadFiletab[] = {
 #ifdef _DEBUG
-    {"_d.pyd", "rb", C_EXTENSION},
+    "_d.pyd",
 #else
-    {".pyd", "rb", C_EXTENSION},
+    ".pyd",
 #endif
-    {0, 0}
+    NULL
 };