- Changes register allocation to only use even numbered registers on Arm.
- Turns on float32 testing in test-gap-resolver.cc.

This is effectively a revert of:
https://codereview.chromium.org/2086653003/

LOG=N
BUG=V8:4124, V8:5202

Review-Url: https://codereview.chromium.org/2176173003
Cr-Commit-Position: refs/heads/master@{#38151}