[Bug libstdc++/66059] make_integer_sequence should use a log(N) implementation

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66059

--- Comment #10 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Adrian Wielgosik from comment #9)
>  TOTAL                 :   0.97             0.01             0.99           
> 119627 kB

By passing in the length of the first sequence instead of using sizeof... the
std::make_integer_sequence result comes down to:

 TOTAL                 :   0.23             0.01             0.25             
15114 kB

Which is very reasonable, and within an order of magnitude of Daniel's, which I
think is good enough (especially if we're going to get a compiler intrinsic
eventually anyway).

But rather than making that change I think the right thing to do is to fix the
front-end so that sizeof... doesn't make such a big difference and we don't
have to jump through hoops to avoid it. I'll file a PR for that tomorrow.