fix(util/thread): warning messages
fix(kernel/expr): expr_cache initialization

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
chore(util/sexpr): cleanup

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>
fix(util/sexpr/options): add workaround for clang++

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>