art: fix boot in art mode

It's a bug in libcore

origin commit is GC triggering performance optimizations
SHA1 ID: 7646e2eb41024d152d76b269653c2321e2cfbd23

URL: https://github.com/CyanogenMod/android_libcore/commit/7646e2eb41024d152d76b269653c2321e2cfbd23

Change-Id: I5ec4ae74dc70f1859db2bae8588e697b147a2682