Bump the minimal version required to compile DMD to 2.076.1

[Stefan Koch]

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

Yes! we cannot keep bumping the version of the compiler, 
personally I find 2.072 rather steep!
really we should be able to build with 2.068.