Fix a microbenchmark crash on mingw32; seemingly %lld is not universally supported on Windows, and %I64d is recommended instead. R=csilvers DELTA=6 (5 added, 0 deleted, 1 changed) Revision created by MOE tool push_codebase. MOE_MIGRATION=1034 git-svn-id: https://snappy.googlecode.com/svn/trunk@18 03e5f5b5-db94-4691-08a0-1a8bf15f6143