feat(build): use Release when compilation mode is not specified
feat(build): do not display WARNING message when tcmalloc is not found
fix(util/thread_script_state): style
fix(frontends/lean/tactic_hint): failure when compiling lean terms into
tactics: mismatch on the number of universe parameters
feat(library/module): provide predicate module::is_definition
refactor(kernel/converter): replace extra_opaque_set with predicate

It gives us more flexibility.