Revert r168411 for now.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@168667 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/AST/Decl.cpp b/lib/AST/Decl.cpp
index 1f390ee..ed48c43 100644
--- a/lib/AST/Decl.cpp
+++ b/lib/AST/Decl.cpp
@@ -777,10 +777,12 @@
         if (llvm::Optional<Visibility> Vis = Function->getExplicitVisibility())
           LV.mergeVisibility(*Vis, true);
       }
-
-      // Note that Sema::MergeCompatibleFunctionDecls already takes care of
-      // merging storage classes and visibility attributes, so we don't have to
-      // look at previous decls in here.
+      
+      if (const FunctionDecl *Prev = Function->getPreviousDecl()) {
+        LinkageInfo PrevLV = getLVForDecl(Prev, OnlyTemplate);
+        if (PrevLV.linkage()) LV.setLinkage(PrevLV.linkage());
+        LV.mergeVisibility(PrevLV);
+      }
 
       return LV;
     }