[DWARF parser] Produce correct template parameter packs

Templates can end in parameter packs, like this

template <class T...> struct MyStruct 
  { /*...*/ };

LLDB does not currently support these parameter packs; 
it does not emit them into the template argument list
at all. This causes problems when you specialize, e.g.:

template <> struct MyStruct<int> 
  { /*...*/ };
template <> struct MyStruct<int, int> : MyStruct<int> 
  { /*...*/ };

LLDB generates two template specializations, each with 
no template arguments, and then when they are imported 
by the ASTImporter into a parser's AST context we get a 
single specialization that inherits from itself, 
causing Clang's record layout mechanism to smash its
stack.

This patch fixes the problem for classes and adds
tests. The tests for functions fail because Clang's
ASTImporter can't import them at the moment, so I've
xfailed that test.

Differential Revision: https://reviews.llvm.org/D33025

llvm-svn: 302833