When we start the definition of a class template, set the

When we start the definition of a class template, set the
InjectedClassNameType's Decl to point at the definition. It's a little
messy, but we do the same thing with classes and their record types,
since much of Clang expects that the TagDecl* one gets out of a type
is the definition. Fixes several Boost.Proto failures.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@102691 91177308-0d34-0410-b5e6-96231b3b80d8