The private clause is the first with 'recipes', so a lot of
infrastructure is included here, including some MLIR dialect changes
that allow simple adding of a privatization. We'll likely get similar
for firstprivate and reduction.
Also, we have quite a bit of infrastructure in clause lowering to make
sure we have most cases we could think of covered.
At the moment, ONLY private is implemented, so all it requires is an
'init' segment (that doesn't call any copy operations), and potentially
a 'destroy' segment. However, actually calling 'init' functions on each
of the elements in them are not properly implemented, and will be in a
followup patch.
This patch implements all of that, and adds tests in a way that will be
useful for firstprivate as well.
The 'cache' construct is an interesting one, in that it doesn't take any
clauses, and is exclusively a collection of variables. Lowering wise,
these just get added to the associated acc.loop. This did require
some work to ensure that the cache doesn't have 'vars' that aren't
inside of the loop, but Sema is taking care of that with a warning.
Otherwise this is just a fairly simple amount of lowering, where each
'var' in the list creates an acc.cache, which is added to the acc.loop.
