On LP32, this makes no difference. Not an ABI change.
On LP64, results are going to be in %rax or x0 whether they're 32- or 64-bit,
and the only difference is going to be whether the top bits are clobbered.
Bug: 18390956
Change-Id: I0bd4496231bdded34c1fa03e895021ac0df7f8e1