Fixes #144 CMake fails without Git

[ulvgard]

With this patch GetGitVersion.cmake checks for the existance of Git before attempting to get Benchmark version from the logs. If Git is not found, the version is set to v0.0.0 as was the default behaviour of the script.

[googlebot]

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[ulvgard]

I signed it!
(Corporation DiracResearch)

[dmah42]

please make sure the author email on the commits matches the expectations from the corporate CLA.

[ulvgard]

The author email is an address associated with our googlegroup which I believe should be sufficient?
Maybee, the CLA must be approved by Google first.

[dmah42]

possibly. we shall wait and see and i'll poke the bear on this side if nothing happens.

[ulvgard]

The CLA was just signed and filed by Google

[ulvgard]

I would also like to remove the CMake message that prints GIT_VERSION?

[dmah42]

@ulvgard sounds good in the case that git isn't available.

[dmah42]

@googlebot he signed it. check again.

[dmah42]

@ulvgard whenever you can, please reply "I signed it!" so googlebot updates.

[ulvgard]

I signed it!
(Corporation DiracResearch)

[dmah42]

the bot still thinks you didn't. maybe the commit author doesn't match expectations?

[ulvgard]

Yep, somehow the email was not related to the googlegroup. Even though I remember registering it. Anyway... Thanks Dominic

[googlebot]

CLAs look good, thanks!

[dmah42]

I just noticed this version bump, but it was released in 2013. Commenting for posterity that it was noticed and approved.