Module Debugging: Fix the condition for determining whether a template

Module Debugging: Fix the condition for determining whether a template
instantiation is in a module.

This patch fixes the condition for determining whether the debug info for a
template instantiation will exist in an imported clang module by:

- checking whether the ClassTemplateSpecializationDecl is complete and
- checking that the instantiation was in a module by looking at the first field.

I also added a negative check to make sure that a typedef to a forward-declared
template (with the definition outside of the module) is handled correctly.

http://reviews.llvm.org/D19443
rdar://problem/25553724

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@267464 91177308-0d34-0410-b5e6-96231b3b80d8