Fixing sys cdevs.h

How to fix sys/cdevs.h error that prevents building on Raspbian

Ivan Drucker submitted this in late October 2015 as #40:

Raspbian Wheezy ships broken, and if you need to build certain things, even after installing build-essential, you can still get an error that ca be fixed with:

sudo apt-get -y install --reinstall libc6-dev

I think (but can't remember for sure) that the A2CLOUD and A2SERVER installer scripts take care of this if necessary, though installing on Debian 7 i386 or Raspbian Wheezy doesn't perform it because the availability of binaries means build-essential is never installed.