Revise the implementation logic of sized deallocation: Do not automatically generate...

Revise the implementation logic of sized deallocation: Do not automatically generate weak definitions of the sized operator delete (in terms of unsized operator delete). Instead, provide the funcitonality via a new compiler flag, -fdef-sized-delete.
The current implementation causes link-time ODR violations when the delete symbols are exported into the dynamic table.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@229241 91177308-0d34-0410-b5e6-96231b3b80d8