Determine C++ Standard Dynamically

[juniperfdel]

The variety of standards used by collaboration members leads to compilation errors which require editing of the Makefile. This pull request adds a very simple shell script which compiles and runs the script found in this stackoverflow answer: https://stackoverflow.com/a/51536462. Make then checks this version against the one ROOT was compiled with to ensure compatibility. Then finally uses the determined C++ standard in the compile flags.

[juniperfdel]

I just noticed that clang++ needs to be supported as well, I don't have a mac so I can't test if the c++ script from the stackoverflow answer works with clang++.

[GernotMaier]

I've looked into this issue and the suggested solution unfortunately does not cover all cases:

• not working on clang++ systems
• the requirement that System's C++ Standard is different than the one compiled with ROOT is too strong; it is quite an effort to recompile root for the only reason that a compiler flag is not consistent

Searching around, it seems there is not really a good solution, e.g., here https://stackoverflow.com/questions/2324658/how-to-determine-the-version-of-the-c-standard-used-by-the-compiler/2324913#2324913

I would leave it for now, my goal was to prepare some docker/singularity container which can be used in most places. This would solve automatically the issue of having to prepare for every possible compiler / system option.

[juniperfdel]

Thanks for looking into the idea