Add "CMake Error at" as an error keyword

[glandium]

[sylvestre]

@sarah-clements @Archaeopteryx what do you think ? seems trivial enough

[Archaeopteryx]

The code would work but adding additional keywords is expensive because every line in every log gets checked against it and only 2 bugs have been logged for such failures in the last 2 years (bug 1736502, bug 1748369). The tasks failed and the issues got caught, keeping the current state without the additional rule looks like the better trade-off.

[jmaher]

@glandium do you have plans to continue working on this, or should we close this PR?