In case libvhost-user is used externally, that projects compiler
warnings might be more strict. Enforce an extra set of compiler warnings
to catch issues early on.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <08daa1896ad8824e17d57d6a970bc0b4bee73ece.1671741278.git.marcel@holtmann.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>