Merging r220874:
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r220874 | hans | 2014-10-29 14:20:57 -0700 (Wed, 29 Oct 2014) | 3 lines

Follow-up to r216619: use isCXXCLassMember() instead of trying to
check the context ourselves when selectively allowing late-added
dll attributes on unused free functions and variables (PR20746)
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git-svn-id: https://llvm.org/svn/llvm-project/cfe/branches/release_35@221253 91177308-0d34-0410-b5e6-96231b3b80d8