When mangling names, always use the canonical decl. Fixes PR5144.

llvm-svn: 83420
diff --git a/clang/lib/CodeGen/Mangle.cpp b/clang/lib/CodeGen/Mangle.cpp
index 7555ae5..702edf0 100644
--- a/clang/lib/CodeGen/Mangle.cpp
+++ b/clang/lib/CodeGen/Mangle.cpp
@@ -1303,7 +1303,7 @@
                                    "Mangling declaration");
     
     CXXNameMangler Mangler(Context, os);
-    if (!Mangler.mangle(D))
+    if (!Mangler.mangle(cast<NamedDecl>(D->getCanonicalDecl())))
       return false;
 
     os.flush();