* module/language/tree-il/analyze.scm (<reference-dag>): New record
type.
(dag-reachable-nodes, dag-reachable-nodes*, unused-variable-analysis):
New variables.
(unbound-variable-analysis): Slightly simplify the `up' procedure.
* module/language/tree-il/compile-glil.scm (%warning-passes): Add
`unused-toplevel'.
* module/system/base/message.scm (%warning-types): Likewise.
* test-suite/tests/tree-il.test (%opts-w-unused-toplevel): New variable.
("warnings")["unused-toplevel"]: New test prefix.
* module/language/tree-il/analyze.scm (<arity-info>): New record type.
(validate-arity, arity-analysis): New variables.
* module/language/tree-il/compile-glil.scm (%warning-passes): Add
`arity-mismatch'.
* module/system/base/message.scm (%warning-types): Likewise.
* test-suite/tests/tree-il.test (read-and-compile): Remove, as it's now
public.
(%opts-w-arity): New.
("warnings")["arity mismatch"]: New test prefix.
