When forming the injected-class-name of a variadic template, the

When forming the injected-class-name of a variadic template, the
template argument corresponding to a template parameter pack is an
argument pack of a pack expansion of that template parameter
pack. Implements C++0x [temp.dep.type]p2 (at least, as much of it as
we can).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@122498 91177308-0d34-0410-b5e6-96231b3b80d8