workaround libuv bug under windows

uwt.sync was broken during the last releases.
It was not captured by the test cases, because the
tests link also uwt that pull in the initialization
code ...

src/uv_fs_sync.ml

@@ -30,6 +30,11 @@ type loop_mode =
 open Uwt_base
 include Fs_types
 
+#if HAVE_WINDOWS <> 0
+external init_uwt : unit -> unit = "uwt_init_sync_na" NOALLOC
+let () = init_uwt ()
+#endif
+
 let wrap x =
   if Int_result.is_error x then
     Error (Int_result.to_error x)

src/uwt_stubs_base.c

@@ -747,11 +747,26 @@ static struct custom_operations ops_uwt_handle_nf = {
 #pragma GCC diagnostic pop
 #endif
 
+#ifdef _WIN32
+CAMLprim value
+uwt_init_sync_na(value unit)
+{
+  (void) unit;
+  /* workaround libuv bug. see #1488 */
+  uv_hrtime();
+  return Val_unit;
+}
+#endif
+
 CAMLprim value
 uwt_init_na(value unit)
 {
   unsigned int i,j;
 
+#ifdef _WIN32
+  uv_hrtime();
+#endif
+
   /* they must point to the same location. Otherwise the
      polymorphic comparison function won't behave as intended */
   ops_uwt_handle.identifier = custom_op_name;

src/uwt_stubs_base.h

@@ -113,6 +113,9 @@ UWT_EXTERN1(uwt_default_loop);
 
 /* memory handling (c heap) */
 UWT_EXTERN1(uwt_init_na);
+#ifdef _WIN32
+UWT_EXTERN1(uwt_init_sync_na);
+#endif
 
 UWT_LOCAL void
 uwt__malloc_uv_buf_t(uv_buf_t *, size_t);