Switch to using psq_run_tool_on_source as opposed to PRE_LINK commands.

This enables us to print more detailed reports of how the checking is
going for each file, instead of having the "link" process appear to
take forever
Merge pull request #17 from smspillaz/clang-tidy-target-cmake.item_17

Switch to using psq_run_tool_on_source as opposed to PRE_LINK commands.