mingw add win32helper to lib and fix extpoll

Based on work from Radu Sorici <soriciradu@gmail.com>

Signed-off-by: Andy Green <andy.green@linaro.org>
diff --git a/lib/libwebsockets.c b/lib/libwebsockets.c
index ebd54ba..9e22a16 100644
--- a/lib/libwebsockets.c
+++ b/lib/libwebsockets.c
@@ -32,6 +32,14 @@
 int openssl_websocket_private_data_index;
 #endif
 
+#ifdef __MINGW32__
+#include "../win32port/win32helpers/websock-w32.c"
+#else
+#ifdef __MINGW64__
+#include "../win32port/win32helpers/websock-w32.c"
+#endif
+#endif
+
 /*
  * In-place str to lower case
  */