Merging r268673:

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r268673 | koriakin | 2016-05-05 21:13:17 +0100 (Thu, 05 May 2016) | 5 lines

[MSan] [MIPS64] Fix vararg helper for >1 fixed argument.

This fixes http://llvm.org/PR27646 on Mips64.

Differential Revision: http://reviews.llvm.org/D19989
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llvm-svn: 271121