Allow <vboot/crossystem.h> to be usable in C++ code.

BUG=None
TEST=build update_engine with a change that uses the header.
BRANCH=none

Change-Id: Icbfe9be615a4f7f4078a0a0cde64324908dea2a7
Reviewed-on: https://chromium-review.googlesource.com/174428
Commit-Queue: Richard Barnette <jrbarnette@chromium.org>
Tested-by: Richard Barnette <jrbarnette@chromium.org>
Reviewed-by: Bill Richardson <wfrichar@chromium.org>
1 file changed