[RFC] cmake: Error instead of warning and dropping invalid LLVM_USE_SANITIZER

[Justin Bogner via llvm-commits]

PEBKAC. I was pointing at a different source directory than I thought
and got confused. This works fine, and I've committed it in r246531.

Alexey Samsonov <vonosmas at gmail.com> writes:
> I'm fine with issuing an error instead of the warning. Not sure why CMake
> doesn't fail with non-zero exit code, though. Does it continue configuring the
> project?
>
> On Mon, Aug 31, 2015 at 5:51 PM, Justin Bogner <mail at justinbogner.com> wrote:
>
>     Typos in LLVM_USE_SANITIZER=<value> emit a fairly missable warning and
>     run with no sanitizers. It would be better to error here, but the
>     attached patch doesn't seem to work (cmake still exits zero). Thoughts?
>
> --
> Alexey Samsonov
> vonosmas at gmail.com