If you had the same issue I did, I suspect that your project builds but code-completion / code highlighting fails? I've just found some notes that may be useful. Here's what I did:
For language 'GNU C++' I added:
For "GNU C" I added:
TBH, I don't think all the directories above are actually required (you could probably remove the 'bits' directories) but the list above worked for me at the time.
I am now using Eclipse Indigo (version 3.7.2) from eclipse.org and it automatically finds and adds the correct include directories. The list is different for me:
Clearly, only add the include directories that actually exist on your system ;-)