A shift by the operand's own width or more is poison in LLVM, not a wrong
number: (<< 1 32) at -O2 compiled to a bare retq. A literal count out of range
is now rejected in check.ml, and emit.ml masks a computed one to width - 1,
which is what the hardware does and which LLVM folds away for a constant.
There is one top-level namespace, but the environment's tables are per-kind, so
only a function was ever checked for a duplicate. (defn item ...) beside
(defvar item ...) type checked and then died in LLVM as a redefinition of
'@flan.item'; two colliding type declarations were not caught anywhere. One
pass over Ast.declared_name now runs before every other collection pass. That
function lives in ast.ml because Load needs the same set - the names an import
renames - and two copies would drift.
