Fix libvhost-user.c compilation.

The source file uses VIRTIO_F_VERSION_1 which is
not defined by <linux/virtio_config.h> on Debian 10.

The system-provided <linux/virtio_config.h> which
does not include the macro definition is included
through <linux/vhost.h>, so fix the issue by including
the standard-headers version before that.

Signed-off-by: David 'Digit' Turner <digit@google.com>
Message-Id: <20230405125920.2951721-2-digit@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

subprojects/libvhost-user/libvhost-user.c

@@ -32,6 +32,12 @@
 #include <sys/mman.h>
 #include <endian.h>
 
+/* Necessary to provide VIRTIO_F_VERSION_1 on system
+ * with older linux headers. Must appear before
+ * <linux/vhost.h> below.
+ */
+#include "standard-headers/linux/virtio_config.h"
+
 #if defined(__linux__)
 #include <sys/syscall.h>
 #include <fcntl.h>