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All 32bit bots now have 64bit kernels and can run 64bit gold. So always use
that.  We already require running 64bit binaries for clang, and the official
bots already used to do this for gold.  This makes linking on 32bit bots faster,
and simplifies our configurations.

BUG=396333
TBR=brettw

Review URL: https://codereview.chromium.org/503873004

Cr-Commit-Position: refs/heads/master@{#291904}