Don't emit the extra checksum into the .gcda file if the user hasn't asked for
it. Fortunately, versions of gcov that predate the extra checksum also ignore
any extra data, so this isn't a problem. There will be a matching commit in
compiler-rt.
Don't emit the extra checksum into the .gcda file if the user hasn't asked for
it. Fortunately, versions of gcov that predate the extra checksum also ignore
any extra data, so this isn't a problem. This matches the API change made in
r176745.