Only download Google Test once.

We can do this on the build step and then pass the result to the
tests so that they can link against a local copy. Speeds up test
time dramatically.
Bump veracpp-cmake submodule version.
Bump cppcheck-target-cmake version.
Set minimum cmake version.
Update cmake-unit.
Merge pull request #24 from smspillaz/common-universal-cmake.item_23

Only download Google Test once.