We have two ways of marking a test as skipped:
- raise MESON_SKIP_TEST
- declare that the tools it needs in test.json are unavailable
Doing the former requires performing the configure stage including e.g.
language setup.
In several cases we weren't even getting this far anyway since we used
both mechanisms (the cmake category has a category-wide skip for this,
in fact). In some case, we were missing test.json declaring it skippable;
add this.
Compiled languages are Meson's bread and butter, but hardly required.
This is convenient, because many test caases specifically, do not care
about testing the compiler interactions.
In such cases, we can skip doing compiler lookups which aren't used, as
they only slow down test setup.