[modules] Don't diagnose a conflict between two using-declarations that name equivalent internal linkage entities.

llvm-svn: 257512
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 4b03baf..11f2329 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -7797,6 +7797,10 @@
       if (UsingShadowDecl *Shadow = dyn_cast<UsingShadowDecl>(*I))
         PrevShadow = Shadow;
       FoundEquivalentDecl = true;
+    } else if (isEquivalentInternalLinkageDeclaration(D, Target)) {
+      // We don't conflict with an existing using shadow decl of an equivalent
+      // declaration, but we're not a redeclaration of it.
+      FoundEquivalentDecl = true;
     }
 
     if (isVisible(D))