[CMake] how to get the version of a library

[brice rebsamen]

How to know the version of an installed library? My code has #if macros 
to handle different APIs. So I would need to get the version and set 2 
variables (MAJOR and MINOR) and pass them to the compiler (-D).

To be more precise, I am interested in Player/Stage. One way to get the 
version is to run the player executable. Under linux:

VERSION=`player 2>&1 | grep "Player v" | cut -d' ' -f2`
this gives "v2.2.0". Then
MAJOR=`echo $VERSION | cut -d'.' -f2`
MINOR=`echo $VERSION | cut -d'.' -f3`

I do not particularly need a solution that would work under windows at 
the moment, but that would be a bonus of course.

Regards,
Brice