block: Workaround for older versions of MinGW gcc

Versions before gcc-4.6 don't support unnamed fields in initializers
(see http://gcc.gnu.org/bugzilla/show_bug.cgi?id=10676).

Offset and OffsetHigh belong to an unnamed struct which is part of an
unnamed union. Therefore the original code does not work with older
versions of gcc.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/win32-aio.c

diff --git a/block/win32-aio.c b/block/win32-aio.c
index c34dc73..92f25a9 100644
--- a/block/win32-aio.c
+++ b/block/win32-aio.c
@@ -167,11 +167,11 @@
         waiocb->is_linear = true;
     }
 
-    waiocb->ov = (OVERLAPPED) {
-        .Offset = (DWORD) offset,
-        .OffsetHigh = (DWORD) (offset >> 32),
-        .hEvent = event_notifier_get_handle(&aio->e)
-    };
+    memset(&waiocb->ov, 0, sizeof(waiocb->ov));
+    waiocb->ov.Offset = (DWORD)offset;
+    waiocb->ov.OffsetHigh = (DWORD)(offset >> 32);
+    waiocb->ov.hEvent = event_notifier_get_handle(&aio->e);
+
     aio->count++;
 
     if (type & QEMU_AIO_READ) {