* CI-unixish.yml: handle precompiled headers with `ccache`
* actually support `ccache` in CMake < 3.17
* CI-unixish-docker.yml: split CMake build and test execution into separate steps
* findDependencies.cmake: only print message about macthcompiler being disabled when it is actually used
* CI-unixish-docker.yml: added missing `ccache` CMake options
* modernized some CMake invocations
* CI-unixish.yml: use `ccache` for Linux gcc CMake builds
* CI-unixish-docker.yml: use `ccache` for Linux gcc CMake builds
* CI-unixish-docker.yml: enabled CMake build with tests for more images
* CI-unixish-docker.yml: adjusted some step checks
* CI-unixish-docker.yml: perform make and CMake builds in parallel
* CI-unixish-docker.yml: cleanups
* CI-unixish-docker.yml: only install necessary packages
Oliver Stöneberg
amai2012