port 19741ac9 (r32301)

  original commit message:
  The Float32RoundTruncate operator rounds float32 numbers towards zero.
  The operator is currently implemented on x64, ia32, arm, and arm64.

  Additionally I added support for the float32 vrintz, vrintn, and vrinta
  instructions to the arm simulator.

BUG=

Review URL: https://codereview.chromium.org/1493213002

Cr-Commit-Position: refs/heads/master@{#32537}