[PATCH v2] Add gdb::nullopt, from C++17's std::nullopt

[Pedro Alves]

On 6/2/20 9:27 PM, Christian Biesinger via Gdb-patches wrote:
> Ping? Simon/Pedro, any thoughts?

As I had said on IRC a few days ago:

<palves>      I remember not including std::nullopt in the original gdb::optional patch for some reason.
<palves>      but I don't remember what reason it was.
<palves>      maybe it was an C++17 inline variable or something.
<palves>      if it works, and the tests pass, I'm happy.  ship it.

BTW, was this implementation borrowed from libstdc++; or put another
way, did you take a look at the implementation from libstdc++, see if
there's anything there taking care of some non-obvious issue, that we
should mimic?

Thanks,
Pedro Alves