Fix sorting of using directives, from Jay Foad

llvm-svn: 72048
diff --git a/clang/lib/Sema/SemaLookup.cpp b/clang/lib/Sema/SemaLookup.cpp
index 8942523..8fe287c 100644
--- a/clang/lib/Sema/SemaLookup.cpp
+++ b/clang/lib/Sema/SemaLookup.cpp
@@ -713,7 +713,7 @@
       AddScopeUsingDirectives(Context, SC, UDirs);
 
   // Sort heapified UsingDirectiveDecls.
-  std::sort_heap(UDirs.begin(), UDirs.end());
+  std::sort_heap(UDirs.begin(), UDirs.end(), UsingDirAncestorCompare());
 
   // Lookup namespace scope, and global scope.
   // Unqualified name lookup in C++ requires looking into scopes