[ASTImporter] Do not import FunctionTemplateDecl in record twice.

Summary:
For functions there is a check to not duplicate the declaration if it is in a
record (class). For function templates there was no similar check, if a
template (in the same class) was imported multiple times the
FunctionTemplateDecl was created multiple times with the same templated
FunctionDecl. This can result in problems with the declaration chain.

Reviewers: martong, a.sidorin, shafik, a_sidorin

Reviewed By: a_sidorin

Subscribers: rnkovacs, dkrupp, Szelethus, gamesh411, cfe-commits

Tags: #clang

Differential Revision: https://reviews.llvm.org/D65203

llvm-svn: 368163