This commit makes cpplint act like the other compiler mirroring tools. It
will always return 0 even if it reports warnings and will only return non
zero if there is a problem running the command. In addition, it will now
add some extra text to allow CTest to recognize the warnings and report
them correctly to CDash.
Create a `<LANG>_CPPLINT` target property (initialized by a
`CMAKE_<LANG>_CPPLINT` variable) to specify a `cpplint` style checker
command line to be run along with the compiler.