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This CL re-lands r405933 and removes the hack that was needed while
rolling in the reworked v8_target_cpu code, but this adds the missing
line that was needed for CrOS to work correctly with their custom
toolchain.

TBR=machenbach@chromium.org, llozano@chromium.org
BUG=593461, 625353

Review-Url: https://codereview.chromium.org/2158143002
Cr-Commit-Position: refs/heads/master@{#406115}