Merging r310522:

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r310522 | belleyb | 2017-08-09 13:58:39 -0700 (Wed, 09 Aug 2017) | 8 lines

[Linker] PR33527 - Linker::LinkOnlyNeeded should import AppendingLinkage globals

Linker::LinkOnlyNeeded should always import globals with
AppendingLinkage.

This resolves PR33527.

Differential Revision: https://reviews.llvm.org/D34448
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llvm-svn: 318180