[patch] replace reinterpret_cast with static_cast in tests

[Paolo Carlini]

Jonathan Wakely wrote:
> No need to use reinterpret_cast in these tests, static_cast is enough.
>  The copies of these tests under 20_util already use static_cast.
>
> Texted x86-64/linux - OK for mainline?
>   
Yes, please!

Thanks,
Paolo.