[PATCH] CMake: extend add_version_info_from_vcs

[Adam Strzelecki]

@Changler Did you had a change to have a look at this patch? It may be useful for Debian/Ubuntu nightly users that currently see sthing like:

$ clang --version
Ubuntu clang version 3.5.0-1~exp1 (trunk) (based on LLVM 3.5.0)
Target: x86_64-pc-linux-gnu
Thread model: posix

Instead exact revision. Of course package has revision inside its name, but still would be nice to have this in --version.

@Sylvestre: Am I right you're using Cmake to do nightlies?

-- 
Adam