New incoming test262 tests check what happens on detached ("neutered")
ArrayBuffers. This patch makes the test262 infrastructure define
detaching an ArrayBuffer in terms of %ArrayBufferNeuter, passing the
--allow-natives-syntax flag, when it is needed.

BUG=v8:4193
LOG=N
R=adamk,machenbach

Review URL: https://codereview.chromium.org/1897203003

Cr-Commit-Position: refs/heads/master@{#35676}