[ASTImporter] Import every Decl in lambda record

Summary:
Previously only the fields were imported. Now every Decl is imported.
This way the destructor decl is not missing after import.

Patch by balazske (Balázs Kéri)

Reviewers: a.sidorin, shafik

Reviewed By: shafik

Subscribers: balazske, cfe-commits, Szelethus, martong, dkrupp

Tags: #clang

Differential Revision: https://reviews.llvm.org/D57740

llvm-svn: 354120