Fix check for LLVM_FORCE_HEAD_REVISION after it was "fixed".

The bots actually use "YES", not "1", and so by trying to
"correctly" enforce it, we actually broke it in r507823 :(.

TBR=brucedawson@chromium.org
TBR=smut@google.com
TBR=thakis@chromium.org
NOTRY=true
BUG=82385, 765859

Change-Id: I4e21cbfe0403bfccbafd08b65a1392093cafc360
Reviewed-on: https://chromium-review.googlesource.com/711219
Commit-Queue: Dirk Pranke <dpranke@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Cr-Commit-Position: refs/heads/master@{#507852}
1 file changed