The current_cpu value was erroneously removed from the build config json.
In multi-arch builds, each toolchain subdirectory in the build-product
output emits its own build-config json, where current_cpu determines
the architecture type of the sub-build.

Correctness-fuzzer runs could wrongly determined x86 sub-builds as x64.

Bug: chromium:777285
Change-Id: I5104630cd8ebbd263d557fb29771a31a2a1d78c2
Reviewed-on: https://chromium-review.googlesource.com/737797Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48950}