Default compiler
From Klaus' wiki
If you want to change the default compiler that is selected by default in eclipses new project wizard do go to the menu and select Windows -> Preferences -> C/C++ -> New C/C++ Project Wizard
In that dialogue choose the preferred toolchain and click on the button "Make toolchain(s) preferred"
Next time you start a new C/C++ project Eclipse will automagically select the correct toolchain.
Thanks to the bright student Lasse Nielsen for the tip.