[v3] Add constexpr specifiers to std::shared_ptr, std::unique_ptr, etc

[Paolo Carlini]

Hi,

> No, your patch didn't effect it, the regression was just introduced by
> the recent constexpr changes, so I was going to fix it as part of
> adding constexpr to unique_ptr. I'll do it separately on Monday.

Ah, ok, great. Sorry if I touched code you were already working on, I'm not concentrating on constexpr at this time, just applying small tweaks here and there which I personally judge uncontroversial enough while going through the code, fixing small issues reported in Bugzilla etc. As usual, thanks a lot for your help.

Paolo