Merging r213733:
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r213733 | kongyi | 2014-07-23 10:25:02 +0100 (Wed, 23 Jul 2014) | 5 lines

ARM: Add doc for ACLE memory barrier intrinsics

Add documentations for ACLE memory barrier intrinsics, describing their motion
barrier characteristics.

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git-svn-id: https://llvm.org/svn/llvm-project/cfe/branches/release_35@213787 91177308-0d34-0410-b5e6-96231b3b80d8