bswap: fix compiler warning

The bswap functions use memcpy but the bswap.h header itself does not seem to
include it in some configuration such as cross compiling for powerpc64
on x86_64 machine.

The patch explicitly includes string.h.
Signed-off-by: NAlexey Kardashevskiy <aik@ozlabs.ru>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: NDavid Gibson <david@gibson.dropbear.id.au>
Reviewed-by: NAndreas Färber <afaerber@suse.de>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

include/qemu/bswap.h

@@ -4,6 +4,7 @@
 #include "config-host.h"
 #include <inttypes.h>
 #include <limits.h>
+#include <string.h>
 #include "fpu/softfloat.h"
 
 #ifdef CONFIG_MACHINE_BSWAP_H