Support for destroying operator delete, per C++2a proposal P0722.

Support for destroying operator delete, per C++2a proposal P0722.

This feature is not (yet) approved by the C++ committee, so this is liable to
be reverted or significantly modified based on committee feedback.

No functionality change intended for existing code (a new type must be defined
in namespace std to take advantage of this feature).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@315662 91177308-0d34-0410-b5e6-96231b3b80d8