Allow all sources, including non C or CXX sources to be checked.

This enables header files to be checked. What we were really trying
to filter out was ghost sources created by add_custom_target, which
we can do easily by just filtering out any source who's last
component matches the target name.
Merge pull request #15 from smspillaz/cppcheck-target-cmake.item_15

Allow all sources, including non C or CXX sources to be checked.