audit: Avoid build failures on systems without renameat

renameat has been deprecated in favor of renameat2 for new ports.  This
allows the audit tests to build on RISC-V.

Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>