Simplify for code-gen on Moar to not keep results.
Simplify loop code-gen on Moar.

Don't need to keep result type of block at this level; it's not what
NQP nor Rakudo need. Means we can convey more void context.
Better NQPcode-gen for $int_a < $int_b and similar
Better convey immediate block void context.
Unbust build on JVM.
Simplify JVM for loop code-gen.
First part of simplifying JVM loop code-gen.

Gets rid of some decision making and, potentially, an instruction or
two per iteration and/or some boxing.