Merging r182364:

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r182364 | d0k | 2013-05-21 02:58:54 -0700 (Tue, 21 May 2013) | 4 lines

X86: When emulating unsigned PCMPGTQ with PCMPGTD, fix the sign bit for the smaller type.

Otherwise we'll get a mix of signed and unsigned compares.
Fixes PR15977.
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llvm-svn: 182413