[modules] A using-declaration doesn't introduce a new entity, just a new name

for an existing entity, and as such a using-declaration doesn't need to
conflict with a hidden entity (nor vice versa).

llvm-svn: 247654

clang/lib/Sema/SemaDeclCXX.cpp

@@ -7821,7 +7821,8 @@ bool Sema::CheckUsingShadowDecl(UsingDecl *Using, NamedDecl *Orig,
       FoundEquivalentDecl = true;
     }
 
-    (isa<TagDecl>(D) ? Tag : NonTag) = D;
+    if (isVisible(D))
+      (isa<TagDecl>(D) ? Tag : NonTag) = D;
   }
 
   if (FoundEquivalentDecl)