Merging r264335:

Merging r264335:
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r264335 | dim | 2016-03-24 21:39:17 +0100 (Thu, 24 Mar 2016) | 17 lines

Add <atomic> to ThreadPool.h, since std::atomic is used

Summary:
Apparently, when compiling with gcc 5.3.2 for powerpc64, the order of
headers is such that it gets an error about std::atomic<> use in
ThreadPool.h, since this header is not included explicitly.  See also:

https://llvm.org/bugs/show_bug.cgi?id=27058

Fix this by including <atomic>.  Patch by Bryan Drewery.

Reviewers: chandlerc, joker.eph

Subscribers: bdrewery, llvm-commits

Differential Revision: http://reviews.llvm.org/D18460

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/branches/release_38@265380 91177308-0d34-0410-b5e6-96231b3b80d8