[CMake] Detecting linux distro?

[Stephen Quinney]

I'm sure I'm not the first person to need to do this but I can't see
an obvious solution. I want to be able to detect which Linux system
the package is building on, i.e. is it Fedora, Debian, Gentoo, etc?
And also beyond that, what version of the distro is it? (e.g. FC6. F9,
Debian 4.0) Can someone point me in the right direction?

Thanks,

Stephen Quinney