configure: check for EFD_NONBLOCK | EFD_CLOEXEC flags

Add check for the EFD_NONBLOCK and EFD_CLOEXEC flags to the
CONFIG_EVENTFD test.
This fixes the following build failure on Fedora 9:

      CC    event_notifier.o
    event_notifier.c: In function `event_notifier_init':
    event_notifier.c:21: error: `EFD_NONBLOCK' undeclared (first use in this function)
    event_notifier.c:21: error: (Each undeclared identifier is reported only once
    event_notifier.c:21: error: for each function it appears in.)
    event_notifier.c:21: error: `EFD_CLOEXEC' undeclared (first use in this function)
    make: *** [event_notifier.o] Error 1
Reviewed-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: NMax Filippov <jcmvbkbc@gmail.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

configure

@@ -2241,7 +2241,7 @@ cat > $TMPC << EOF
 
 int main(void)
 {
-    int efd = eventfd(0, 0);
+    int efd = eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC);
     return 0;
 }
 EOF