Fix Clang-tidy modernize-use-nullptr warnings in examples and include directories; other minor cleanups.

Patch by Eugene Zelenko!

Differential Revision: http://reviews.llvm.org/D13172

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@248811 91177308-0d34-0410-b5e6-96231b3b80d8
27 files changed