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

[Jean-Marc Lasgouttes]

Le 03/11/2020 à 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?

JMarc