This should improve the CI response time, as we now (potentially)
perform iwyu and clang-tidy in parallel.

This adds yet another target "smoke-test-suite", which just runs all
tests in the 'smoke' test suite. The static-analysis target was
changed to include *all* static analysis thingies we have, even 'doc'
as Doxygen does also do some checks that the documentation is
"correct".

The smoke-test target is also kept, as it allows developers to simply
run all smoke tests. Furthermore, this adds some missing PHONY
declarations in the Makefile.

The gitlab-ci now runs the smoke-test-suite and static-analysis
targets in two different jobs. Previously the smoke-test would also
run the static-analysis target, which was not intended.

The 'static-analysis' Make target runs all static analysis we
currently have. This allows to run at least static analysis, in cases
where we are able build a particular EMPER configuration, but no able
to execute it (e.g. because the kernel lacks io_uring support).

Fixes #8.

Also move setup.sh from scripts/ to tools/.

and not Make

to allow for e.g. "make VERBOSE=1"