This is instead of explicit control flow which may interfere with branch prediction.  However, explicit control flow is still needed for types other than i16 and i32, due to cmov limitations.

The assembler for cmov is extended to allow the non-dest operand to be a memory operand.

The select lowering is getting large enough that it was in our best interest to combine the default lowering with the bool-folding optimization.

BUG= https://code.google.com/p/nativeclient/issues/detail?id=4095
R=jvoung@chromium.org

Review URL: https://codereview.chromium.org/1125323004