[wing] fix build on x86 architecture

[Silvio Lazzeretti <silviol src gnome org>]

commit 176b349580478e948bbc4fa37f70d6c82116306a
Author: Silvio Lazzeretti <silviola amazon com>
Date:   Wed Dec 5 10:03:01 2018 +0100

    fix build on x86 architecture

 wing/wingnamedpipeconnection.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/wing/wingnamedpipeconnection.c b/wing/wingnamedpipeconnection.c
index 1aa3852..bfd0d5c 100644
--- a/wing/wingnamedpipeconnection.c
+++ b/wing/wingnamedpipeconnection.c
@@ -80,7 +80,7 @@ static GParamSpec *props[LAST_PROP];
 
 G_DEFINE_TYPE (WingNamedPipeConnection, wing_named_pipe_connection, G_TYPE_IO_STREAM)
 
-static void
+static void CALLBACK
 threadpool_io_completion (PTP_CALLBACK_INSTANCE instance,
                           PVOID                 ctxt,
                           PVOID                 overlapped,