Build fix for AIO (-dummy) on Windows, by Stefan Weil.

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@2264 c046a42c-6fe2-441c-8c8c-71466251a162

block-raw.c

@@ -1137,6 +1137,10 @@ void qemu_aio_poll(void)
 {
 }
 
+void qemu_aio_flush(void)
+{
+}
+
 void qemu_aio_wait_start(void)
 {
 }