Reverted in r231254 due to a self-hosting crash of Clang (see Clang
PR22793). Workaround the crash by using {} instead of = default to
define a dtor.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@231274 91177308-0d34-0410-b5e6-96231b3b80d8