* test: assert compiler aliases, llvm tools and cmake-format location in the C++ stack

* feat(cpp-tools)!: pin GEF and turn it off by default

GEF is downloaded from a fixed GitHub release and checked against a
SHA-256 hash.

BREAKING CHANGE: installGef now defaults to false

* fix(cpp-tools): install after python-venv and pin cmake-format

* fix(llvm): install libclang-rt and the llvm meta package, register llvm tool names

* fix(apt-mirror): keep the updates suite and use https with http fallback

* fix(gcc): register cc, c++ and gcov alternatives