PATCH to enable testing C++17 by default

[Marek Polacek]

On Wed, Oct 17, 2018 at 03:19:42PM -0600, Jeff Law wrote:
> On 10/17/18 1:31 PM, Marek Polacek wrote:
> > As discussed in <https://gcc.gnu.org/ml/gcc-patches/2018-10/msg00752.html> it
> > seems to be a high time we turned on testing C++17 by default.
> > 
> > The only interesting part is at the very end, otherwise most of the changes is
> > just using { target c++17 } instead of explicit dg-options.  Removing
> > dg-options has the effect that DEFAULT_CXXFLAGS comes in play, so I've removed
> > a bunch of stray semicolons to fix -Wpedantic errors.
> > 
> > I wonder if we also want to enable 2a, but the overhead could be too much.  Or
> > use 2a instead of 17?
> > 
> > Bootstrapped/regtested on x86_64-linux, ok for trunk?
> > 
> > 2018-10-17  Marek Polacek  <polacek@redhat.com>
> > 
> > 	* g++.dg/*.C: Use target c++17 instead of explicit dg-options.
> > 	* lib/g++-dg.exp: Don't test C++11 by default.  Add C++17 to
> > 	the list of default stds to test.Given this follows Jason's recommendations from the thread, OK for the
> trunk.
> 
> I'll leave it up to Jason to decide when to add 2a and whether or not to
> drop something at that time.

Hearing no objections, I've now committed the patch.

Marek