For now, always use donna32 on msvc

src/win32/orconfig.h

@@ -250,3 +250,6 @@
 #define SHARE_DATADIR ""
 #define HAVE_EVENT2_DNS_H
 #define HAVE_EVENT_BASE_LOOPEXIT
+#define CURVE25519_ENABLED
+#define USE_CURVE25519_DONNA
+