Change task stealing to always get task from head of victim's deque.
Change task stealing to always get task from head of victim's deque.

Differential Revision: https://reviews.llvm.org/D26187

git-svn-id: f99161ee8ccfe2101cbe1bdda2220bce2ed25485@285833 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/openmp,llvm-mirror/openmp,llvm-mirror/openmp,llvm-mirror/openmp,llvm-mirror/openmp