Bump the minimal version required to compile DMD to 2.076.1

[Joakim]

On Friday, 12 January 2018 at 16:13:39 UTC, Seb wrote:
> Motivation
> ----------
>
> 1) It's required for Walter's work on using -betterC for the 
> backend conversion:
>
> https://github.com/dlang/dmd/pull/6907

Not really, he just wants to dogfood betterC on the dmd backend 
when it's ported to D.

> 2) We start to run into random failures lately, e.g.
>
> https://github.com/braddr/d-tester/issues/63
> https://github.com/dlang/dmd/pull/7569#issuecomment-356992048

Seem like issues with 32-bit OS X instead.

> 3) There's also WIP to move dmd-cxx to 2.076.1:
>
> https://github.com/dlang/dmd/pull/7595

No idea when that will be ready.

> So if we have to bump the minimal dmd version required to build 
> DMD anyways for (1), let's be clear about it and state it.
>
> Anyone objecting?

This is going to require changes to ldc/gdc CI, as they actually 
maintain and test against that last C++ version of the common D 
frontend.  It will also affect ports to new platforms, as it 
presents another hoop to jump through.

I see little reason to jump now.  If it's done, it needs to be 
clearly documented.