Try x64 binary for symupload

symupload is still failing for chrome_child.dll on the 32 bit official
bots. One last try of making an x64 binary instead, and then I'm going
to give up.

TBR=mark@chromium.org
BUG=678874, 696257, 696671, 696911,697638

Review-Url: https://codereview.chromium.org/2723233003
Cr-Commit-Position: refs/heads/master@{#454089}