arch: allow the regselector to process nullary nodes created in subregions
arch: allow the regselector to process nullary nodes created in subregions

This is necessary in order to ensure that all outgoing edges of nullary
nodes get a regvalue associated with it. Before this happened only for
nullary nodes created in the root region.

Signed-off-by: Helge Bahmann <c5618920f622561f9c0ec5c42219c4c08180149f@chaoticmind.net>

phate/jive,phate/jive,phate/jive