I made a sample project of using CMake to build an Irrlicht project. Note that this is NOT a way to build Irrlicht using CMake; rather, you should already have built and installed the Irrlicht library for your system. This is a project with the necessary CMake files and a modification of the Irrlicht Hello World sample.
I posted it as a public Github repository, so feel free to browse the source, make contributions/fixes (issue a pull request), etc.
https://github.com/Ricket/IrrlichtCMake
I've successfully used this on a MacBook Pro (OS X Lion) and my netbook (Arch Linux).