eclipse needs definitions to build feisty meow properly

[Fred T. Hamster]

flags like UNIX need to be defined. what's the best way to turn those on? better if we don't have to do anything manual in setting up the project.
basic method is: in project properties, add to the c++ preprocessor symbols these definitions:

name: UNIX value: {leave empty}

can we set this by default for all projects on unix? no. because there are lots of little things that get flipped for different systems and build scenarios.
need this to be automatic though, so code does the right stuff, just by default.