Add clean-test-properties build scripts for linux

With clean-test-properties#6 (closed) resolved we can build clean-test-properties using just the clean compiler (and platform) as a dependency. This requires today's changes to platform, so it will work from Thursday onwards.

For Mac and Windows, this won't work immediately. To fix this:

• Change the clean-compiler*main*Unix path in the project file
• Change the Makefile to build the right main subdirectory as well

I can have a look at this when I'm back, but this is just here so that you know what has to be done if somebody wants it earlier.