Fix iovec probe on OpenBSD

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6297 c046a42c-6fe2-441c-8c8c-71466251a162

configure

@@ -1000,7 +1000,9 @@ fi
 ##########################################
 # iovec probe
 cat > $TMPC <<EOF
+#include <sys/types.h>
 #include <sys/uio.h>
+#include <unistd.h>
 int main(void) { struct iovec iov; return 0; }
 EOF
 iovec=no