[ASTImporter] Import additional flags for functions.

Summary:
At AST import of function delcarations import the flags for defaulted
and deleted.

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/D65999