[RFC] Update C++ standard from 14 to 17

Currently, CIRCT is using C++14 standard.

In this PR, std::variant (a C++17 feature) is desired to build an iterator dispatcher. Thus I’m thinking of updating the C++ standard from 14 to 17 in CIRCT. I’m wondering is there any comment on this?

For your reference, in LLVM, the Flang sub-project is using C++17.

Thanks,
Hanchen

I am +1 on moving up to C++17.

I have no concerns with going up to C++17 so long as it is supported by MSVC or whatever compiler people use on Windows.

As (I would imagine) the sole windows guy, I have no concerns about upgrading to '17.

+1 for C++17!