[LyX/master] Make it possible to select C++ standard with autoconf

[Pavel Sanda]

On Tue, Nov 03, 2020 at 04:30:38PM +0100, Jean-Marc Lasgouttes wrote:
> Le 03/11/2020 ?? 16:16, Pavel Sanda a écrit :
> >>checking for a good C++ mode... none
> >>configure: error: Cannot find suitable mode for compiler g++
> >>make: *** [Makefile:502: config.status] Error 1
> >
> >looking at the log I see:
> >g++: error: unrecognized command line option '-std=gnu++14,11'
> >Seems like wrong argument?
> 
> Embarrassing last minute change. Better now?

Yes, fixed. Thanks, Pavel