Merge branch 'ps/ci-meson'

Merge branch 'ps/ci-meson'

The meson-build procedure is integrated into CI to catch and
prevent bitrotting.

* ps/ci-meson:
  ci: wire up Meson builds
  t: introduce compatibility options to clar-based tests
  t: fix out-of-tree tests for some git-p4 tests
  Makefile: detect missing Meson tests
  meson: detect missing tests at configure time
  t/unit-tests: rename clar-based unit tests to have a common prefix
  Makefile: drop -DSUPPRESS_ANNOTATED_LEAKS
  ci/lib: support custom output directories when creating test artifacts