We don't enforce the -Wsign-conversion CPPFLAG, but it doesn't hurt
to avoid this warning:
warning: implicit conversion changes signedness: 'int' to 'size_t' (aka 'unsigned long') [-Wsign-conversion]
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20191209095002.32194-4-philmd@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>