Fix unportable printf format introduced in commit 9290ad198.

Fix unportable printf format introduced in commit 9290ad198.

"%ld" is not an acceptable format spec for int64 variables, though
it accidentally works on most non-Windows 64-bit platforms.  Follow
the lead of commit 6a1cd8b92, and use "%lld" with an explicit cast
to long long.  Per buildfarm.