[Builtin] Adds return value to builtin selection

src/plugins/builtin/builtin_builder.ml

src/plugins/builtin/builtin_builder.mli

src/plugins/builtin/memcmp.ml

src/plugins/builtin/memcpy.ml

src/plugins/builtin/memmove.ml

src/plugins/builtin/memset.ml

src/plugins/builtin/transform.ml