Change d1b09dba45c4b3ee0f31cd9bbf6941f17afd48f0 removed the
support to detect the C++ version the compiler used by
default. In essence, it forced the compiler in C++11 mode,
if the default was still C++98.
This change reimplements the functionality in the new
configuration system.
Change-Id: Ib4bf7ade85288776f9ae2a870f19764df727e0a5
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>
091df96fb8