This is a follow-up on r174446, now taking Atom processors into

account. Atoms use LEA for updating SP in prologs/epilogs, and the
exact LEA opcode depends on the data model.

Also reapplying the test case which was added and then reverted
(because of Atom failures), this time specifying explicitly the CPU in
addition to the triple. The test case now checks all variations (data
mode, cpu Atom vs. Core).

llvm-svn: 174542