Allow force of old cmake style build for projects that use "project" instead of "gaudi_project"

The logic to select which CMake build style to use is bound to the presence of the call to find_package(GaudiProject) in the top level CMakeLists.txt file.

We have at least one case where this logic is not correct: LHCbIntegrationTests.

We need a way to tell the CMake style selection logic that a project must use the old style even if it looks like it's new.