De-virtualize or remove some methods that have no overrides nor override anything. In some cases remove all together if there are no callers either.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207610 91177308-0d34-0410-b5e6-96231b3b80d8
[C++11] Use 'nullptr' in tablegen output files.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@207611 91177308-0d34-0410-b5e6-96231b3b80d8