Rewrite _validate_cppcheck in terms of a new FindCPPCheck.cmake find macro.

FindCPPCheck uses tooling-find-package-cmake-util.
Merge pull request #26 from smspillaz/cppcheck-target-cmake.item_25

Rewrite _validate_cppcheck in terms of a new FindCPPCheck.cmake find macro. FindCPPCheck uses tooling-find-package-cmake-util.