The EMPER option Meson option for stats is called 'stats' not
'worker_stats'.

This required that we backport iwyu_tool.py from
https://github.com/include-what-you-use/include-what-you-use/pull/891
into tools/, which supports --load.

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

LockedSemaphore is the already existening Semaphore using
a mutex and a condition variable.
PosixMutex is a thin wrapper around a POSIX semaphore.
SpuriousFutexSemaphore is a atomic/futex based implementation
prune to spurious wakeups which is fine for the worker wakeup usecase.

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).

This also changes emper_log so that a std::ostringstream is used to
assemble the log message.

Co-authored-by: Florian Fischer <florian.fl.fischer@fau.de>

And fix the #include issues reported by the newer IWYU version.

The default flavor is the preferred way to use the userspace library it uses
the sys_membarrier syscall or falls back to using userspace membarriers.

This adds the liburcu dependency which must be installed regardless the
'liburcu' meson option.