[PATCH] Add support for -funsigned-bitfields

[Tim Northover]

Hi Artyom,

> C++1y does indeed forbid such implementation, so the flag will need to be
> rejected in -std=c++1y

I'm sure Richard will be along with the full details later, but as I
recall we apply Defect Reports on the language (as opposed to
features) retroactively, on the grounds that the original standard was
broken in such cases.

This one comes from
http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#739,
which makes it fairly clear there would be serious issues with
allowing it.

Cheers.

Tim.