Properly invoke CTest

[sw]

The CMakeLists.txt used enable_testing() without including CTest. This then caused the following errors to be printed:

[proc] Executing command: /home/i/.local/bin/ctest -j6 -C Debug -T test --output-on-failure
[ctest] Cannot find file: /home/i/coding/llama.cpp/build/DartConfiguration.tcl
[ctest] Cannot find file: /home/i/coding/llama.cpp/build/DartConfiguration.tcl

The proper way to use CTest is to include(CTest), which automatically invokes enable_testing() and DartConfiguration.tcl gets generated.