Removed zeroing th.th_task_state for master thread at start of nested parallel.
The th.th_task_state for the master thread at the start of a nested parallel
should not be zeroed in kmp_allocate_team() because it is later put in the
stack of states in kmp_fork_call() for further re-use after exiting the
nested region. It is zeroed after being put in the stack.
Differential Revision: http://reviews.llvm.org/D13702