c++: ICE with alias in pack expansion [PR103769]

This was breaking because when we stripped the 't' typedef in s<t<Args>...>
to be s<Args...>, the TYPE_MAIN_VARIANT of "Args..." was still
"t<Args>...", because type pack expansions are treated as types.  Fixed by
using the right function to copy a "type".

	PR c++/99445
	PR c++/103769

gcc/cp/ChangeLog:

	* tree.cc (strip_typedefs): Use build_distinct_type_copy.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/variadic-alias5.C: New test.

gcc/cp/tree.cc

@@ -1791,7 +1791,7 @@ strip_typedefs (tree t, bool *remove_attributes, unsigned int flags)
 	      Ts pack, resulting in an error.  */
 	    if (type != pat && uses_parameter_packs (type))
 	      {
-		result = copy_node (t);
+		result = build_distinct_type_copy (t);
 		PACK_EXPANSION_PATTERN (result) = type;
 	      }
 	  }

gcc/testsuite/g++.dg/cpp0x/variadic-alias5.C

@@ -0,0 +1,9 @@
+// PR c++/103769
+// { dg-do compile { target c++11 } }
+// { dg-additional-options "--param=hash-table-verification-limit=1000" }
+
+template <typename T> using t = T;
+template <typename...> struct s {};
+template <typename...Args> s<t<Args>...> f() { return {};}
+
+int main() { f<void>(); }