Create a rsimp attribute named attr_name, the attribute declaration is named attr_decl_name.
The cached hinst_lemmas structure is built using the lemmas marked with simp attribute simp_attr_name,
but not marked with ex_attr_name.
We say ex_attr_name is the "exception set". It is useful for excluding lemmas in simp_attr_name
which are not good or redundant for ematching.