Do not do raw name replacement when FromDecl is a class forward-declaration.

Summary:
If the `FromDecl` is a class forward declaration, the reference is
still considered as referring to the original definition given the nature
of forward-declarations, so we can't do a raw name replacement in this case.

Reviewers: bkramer

Subscribers: cfe-commits, klimek

Differential Revision: https://reviews.llvm.org/D27132

llvm-svn: 287929