cmake forces C++11 even if we ask C++14 in tulip5

[rgiot]

The following command

cmake ~/src/tulip5 -DCMAKE_CXX_COMPILER=g++ -DCMAKE_CXX_FLAGS=-std=gnu++14 -DCMAKE_INSTALL_PREFIX=/mnt/data/opt/tulip5release -DCMAKE_BUILD_TYPE=Release

is supposed to ask to build tulip5 with a c++14 compiler (at least it works well like that on tulip4).

Sadly it is not the case as I obtain such kind of errors while compiling my plugins:

... error: use of ‘auto’ in lambda parameter declaration only available with -std=c++14 or -std=gnu++14
             [](const auto &a, const auto &b) {