[ASTImporter] Fix importing OperatorDelete from CXXConstructorDecl

Summary:
Shafik found out that importing a CXXConstructorDecl will create a translation unit that
causes Clang's CodeGen to crash. The reason for that is that we don't copy the OperatorDelete
from the CXXConstructorDecl when importing. This patch fixes it and adds a test case for that.

Reviewers: shafik, martong, a_sidorin, a.sidorin

Reviewed By: martong, a_sidorin

Subscribers: rnkovacs, cfe-commits

Differential Revision: https://reviews.llvm.org/D56651

llvm-svn: 351849