Debug Info: Remove unused code. The MInsn of an _abstract_ variable is
never used again and updating the abstract variable for each inlined
instance of it was questionable in the first place.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209829 91177308-0d34-0410-b5e6-96231b3b80d8
[ADT] Delete the Twine assignment operator

This makes it slightly harder to misuse Twines.  It is still possible to
refer to destroyed temporaries with the regular constructors, though.

Patch by Marco Alesiani!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@209832 91177308-0d34-0410-b5e6-96231b3b80d8