cpu: include set in o3/commit_impl.
cpu: include set in o3/commit_impl.

While the majority of compilers seemed to pickup set from else where,
one version of gcc 4.7 complains, so explictly add it.

andrewfu0325/gem5-aladdin,andrewfu0325/gem5-aladdin,andrewfu0325/gem5-aladdin,andrewfu0325/gem5-aladdin,andrewfu0325/gem5-aladdin,andrewfu0325/gem5-aladdin,andrewfu0325/gem5-aladdin