Add --build-dependencies to ./run scripts to automatically build whatever is neede dto run

[cirosantilli]

Currently in LKMC d53ffcff18aa26d24ea34b86fb80e4a5694378dc for tests is is already a bit wonky to determine what has to be built.

What we have to do is to have a full proper dependency graph, and when user does:

./run --build-dependencies

it automatically downloads and builds whatever is needed.

Then we can get rid of ./build and everyone will be happy.

The gem5 2019 new build system basically does that for gem5 builds alone: https://stackoverflow.com/questions/52279971/how-to-run-the-gem5-unit-tests