Slicing an array whose dimension is a def constant gave len 0 — the
default-hi and cgbasecap arms only read an N_INTLIT dimension. Route
the dimension through the type table (one root, four arms: default-hi
and cgbasecap, local and global each), byte-identical for the def-dim
SLICE shape. The def-dim array .len/.ptr FIELD-read keeps the
N_INTLIT-only limitation — filed as task #56 (cgdot sibling).
Review item #21.
