Use C++ 17

[ringabout]

Merge nim-lang/Nim#17375

Initialization of parent struct in C++ appeared only in C++17.

It solves many issues. As a bonus the compiler itself can be bootstrapped by --gc:orc -b:cpp.
fix nim-lang/Nim#18410
fix nim-lang/Nim#17351
A workaround can be removed: nim-lang/Nim#18836 (comment)

[alaviss]

C++ backend is on the flaky side. We don't even know what are its expectations and what is the generator design.

I'd say changes to it will be on very low priority.

[disruptek]

I see two issues enumerated and it's impossible to know how many issues will be introduced. I think we have to ignore the backends until they are the weak link; garbage in, garbage out, right.

Though I admit that I do wish the cpp backend worked more often, and I'm curious if this could help CPS's C++ codegen issues. 😬

[saem]

I see two issues enumerated and it's impossible to know how many issues will be introduced. I think we have to ignore the backends until they are the weak link; garbage in, garbage out, right.

I totally agree that this is very low priority and I've got no interest in supporting knock on effects. Guess that means that the near term mission needs further clarification.

[saem]

@xflywind can you reread the readme to see what's the mission right now and based on your understanding do one of the following:

• start a discussion asking to expand the scope and how you'll support that expansion
• open an issue, asking to clarify the near term mission, along with your current interpretation

I'd like to avoid doing this issue by issue stuff, as that's painful for everyone, and at the same time want to make sure you're heard and vice versa.

[ringabout]

Fair enough. The alternative way is nim-lang/Nim#18836 to workaround one of the issues.