Let using directives refer to namespace aliases. Fixes PR5479.

llvm-svn: 89657
diff --git a/clang/test/SemaCXX/using-directive.cpp b/clang/test/SemaCXX/using-directive.cpp
index 3b67c7a..51f347d 100644
--- a/clang/test/SemaCXX/using-directive.cpp
+++ b/clang/test/SemaCXX/using-directive.cpp
@@ -102,3 +102,13 @@
     (void)X(); // expected-error{{reference to 'X' is ambiguous}}
   }
 }
+
+// PR5479
+namespace Aliased {
+  void inAliased();
+}
+namespace Alias = Aliased;
+using namespace Alias;
+void testAlias() {
+  inAliased();
+}