Merging r309875:

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r309875 | jlpeyton | 2017-08-02 13:06:32 -0700 (Wed, 02 Aug 2017) | 11 lines

Move lock acquire/release functions in task deque cleanup code

The original locations can be reached without initializing the lock variable
(td_deque_lock), so it is potentially unsafe.  It is guaranteed that the lock
is initialized if the deque (td_deque) is not NULL, and lock functions can be
safely called.

Patch by Hansang Bae

Differential Revision: https://reviews.llvm.org/D36017

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llvm-svn: 318171