Merging r143863:

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r143863 | chandlerc | 2011-11-05 23:59:15 -0700 (Sat, 05 Nov 2011) | 4 lines

This test was assuming that /usr/include was in the system header search
path. That assumption should never have been true, but it was until
I fixed it. Now that its fixed, add a triple here to get correct
behavior even on Windows.
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llvm-svn: 143945