Uses LCOV for C(++) line coverage and Valgrind's Callgrind tool to generate assembly-level line coverage for the generated assembly code. BUG=590332 Change-Id: Ic70300a272c38f4fa6dd615747db568aa0853584 Reviewed-on: https://boringssl-review.googlesource.com/7251 Reviewed-by: David Benjamin <davidben@google.com>