All 3Ps include dirs are treated as SYSTEM, this will stop compilers
stop emitting warnings from those files and greatly helps having high
warning levels and not being swamped by warnings that come from
external libraries.
but it's safer and saner to put the LL 3ps under the ll:: prefix.
This also allows means it is possible to get rid of that bad "if( TRAGET ...) return() endif()" pattern and rather use include_guard().
Nicky