[OPENMP50]Allow functions in declare variant directive to have different
C linkage.

After some discussion with OpenMP developers, it was decided that the
functions with the different C linkage can be used in declare variant
directive.

llvm-svn: 374057
diff --git a/clang/lib/Sema/SemaOpenMP.cpp b/clang/lib/Sema/SemaOpenMP.cpp
index b0fd6aa..ff7e1c0 100644
--- a/clang/lib/Sema/SemaOpenMP.cpp
+++ b/clang/lib/Sema/SemaOpenMP.cpp
@@ -5109,7 +5109,8 @@
           PartialDiagnosticAt(VariantRef->getExprLoc(),
                               PDiag(diag::err_omp_declare_variant_diff)
                                   << FD->getLocation()),
-          /*TemplatesSupported=*/true, /*ConstexprSupported=*/false))
+          /*TemplatesSupported=*/true, /*ConstexprSupported=*/false,
+          /*CLinkageMayDiffer=*/true))
     return None;
   return std::make_pair(FD, cast<Expr>(DRE));
 }