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

llvm-svn: 257512
diff --git a/clang/test/Modules/Inputs/using-decl-redecl/d.h b/clang/test/Modules/Inputs/using-decl-redecl/d.h
new file mode 100644
index 0000000..2243de1
--- /dev/null
+++ b/clang/test/Modules/Inputs/using-decl-redecl/d.h
@@ -0,0 +1 @@
+#include "a.h"