- Modifies LinkageAllocator to understand aliasing on ARM.
- Adds ability to allocate SIMD registers too. Before, these would
  default to stack allocated.
- Modifies WasmCompiler to be platform-independent.

Bug: v8:7754
Change-Id: I0c4355a44a4f409053b51ff675521a465e38aeb8
Reviewed-on: https://chromium-review.googlesource.com/1141114Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#54533}