[Diffusion] rL306858: Completely disable git/svn version checking if not needed.

[Rafael Avila de Espindola via llvm-commits]

It was, yes.

Sorry, I forgot to add that bit to the commit message.

The rationale is that since now disabling the option disables all uses
of the git/svn revision, it should be on by default since some of the
uses were on by default before.

Cheers,
Rafael

Dimitry Andric via Phabricator <reviews at reviews.llvm.org> writes:

> dim added inline comments.
>
> /llvm/trunk/CMakeLists.txt:209 Was it intended to turn this option on by default?  E.g, before this change, llvm's config.h contained just:
>
>     #define LLVM_VERSION_STRING "5.0.0svn"
>
> After this, it contains:
>
>     #define LLVM_VERSION_STRING "5.0.0svn-r306956"
>
> How does that prevent unnecessary rebuilding?
>
> Users:
>   rafael (Author)
>
> https://reviews.llvm.org/rL306858