(reason for revert/reland: patch incorrectly left --vector-stores flag
 on, helpfully revealing some gcstress issues to look at, but they
 don't need to block this CL).

Some pretty hacky code was used to carry out the tail-call
handler dispatch on ia32 vector stores due to a lack
of free registers. It really tanks performance. A better
approach is to use a virtual register on the isolate.

BUG=
TBR=jkummerow@chromium.org, vogelheim@chromium.org

Review URL: https://codereview.chromium.org/1346573002

Cr-Commit-Position: refs/heads/master@{#30737}