Merging r155910:

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r155910 | chapuni | 2012-05-01 03:51:55 -0700 (Tue, 01 May 2012) | 1 line

clang/test/Rewriter/rewrite-modern-extern-c-func-decl.mm: Remove XFAIL and add -U__declspec. mingw32 tends to define built-in __declspec.
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llvm-svn: 156674