Feature/compiler only one version stem

[degauden]

This change align the build system with the Elements 6 series

• the BINARY_TAG is only using the major version of the compiler
• the ElementsBuildFlags has been removed and the local overrides can be performed in the LocalBuildFlags.cmake file.

[mkuemmel]

Thanks!

On the other hand maybe that particular switch should be dropped in SE++. Version 1.67 which provides the numerical differentiation is out since almost 4 years now and should have arrived in all major distros. Also the conda version includes a modern boost version.

[marcschefer]

The problem isn't that we check the version, we need to fix it to work as it's supposed to since it's probable that we'll need version checks for other things in the future. Removing the check would not solve anything.

[degauden]

The switch (Boost_NO_BOOST_CMAKE=ON) has still to be present since Boost has changed its default way to expose cmake-wise its build interface. If I remember correctly, it uses the CMake interface feature that Elements is not supporting (yet). The switch forces the use of the old behavior.

The change in Elements has to be done. But it is nowhere trivial

[marcschefer]

Anyway, seems good to merge to me

[mkuemmel]

Even on my Ubuntu system I don't have to set the CMAKEFLAGS anymore, and the Elements default does work.