re PR c++/33342 (ICE in dependent_type_p, at cp/pt.c:15081)

        PR c++/33342
        * pt.c (most_specialized_class): Set processing_template_decl
        while tsubsting partial spec args.

From-SVN: r128286

gcc/testsuite/g++.dg/template/mem-partial3.C

+// PR c++/33342
+
+template <bool B, class T = void>
+struct enable_if_c {
+  typedef T type;
+};
+
+template <class T>
+struct A
+{
+  template <class U, class V>
+  struct B;
+
+  template <class U>
+  struct B<U, typename enable_if_c<U::sub::value==0>::type>
+  { };
+};
+
+struct C
+{
+  struct sub
+  {
+    static const int value = 0;
+  };
+};
+
+    
+A<int> a;
+A<int>::B<C, void> b;