When checking the redeclaration context of a typedef that refers to a
tag of the same name, compare the lookup contexts rather than the
actual contexts. Fixes PR6923.

llvm-svn: 102437
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index d9696d9..fcee68d 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -5029,7 +5029,8 @@
         if (const TagType *TT = TD->getUnderlyingType()->getAs<TagType>()) {
           TagDecl *Tag = TT->getDecl();
           if (Tag->getDeclName() == Name &&
-              Tag->getDeclContext()->Equals(TD->getDeclContext())) {
+              Tag->getDeclContext()->getLookupContext()
+                          ->Equals(TD->getDeclContext()->getLookupContext())) {
             PrevDecl = Tag;
             Previous.clear();
             Previous.addDecl(Tag);