COMP: fix compilation of examples with clang 7

Bump the minimum required version of Cmake for Examples. It implicitly sets the policy version and allows to configure without error with Clang7.

The problem was that CMAKE_CXX_COMPILE_FEATURES were not detected.

mentioned in issue #1722 (closed)

I didn't know we supported building example as a standalone project. good to know.

merged

mentioned in commit e40fdff9

changed milestone to %7.0.0