Looking into #8584's [win32 build log](http://buildbot.rust-lang.org/builders/auto-win-32-opt/builds/992), no "jemalloc" is found in stdio log. (linux buildbot builds jemalloc well.) Same for [recent build log](http://buildbot.rust-lang.org/builders/auto-win-32-opt/builds/1006) too. Maybe jemalloc is broken (#8731) on windows but is just skipped for unknown reason. (I failed to build rust on windows due to jemalloc errors.)