Remove hard-coded framework test skip logic in skippable(), instead
annotate test.json with environments in which skip is expected.
(Mainly this is done with by testing the value of MESON_CI_JOBNAME now
set for linux jobs)
D lang compilers have an option -release (or similar) which turns off
asserts, contracts, and other runtime type checking. This patch wires
that up to the b_ndebug flag.
Fixes#7082