Fix assert/crash on invalid with __builtin_constant_p conditionals in constant expressions.


git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@221942 91177308-0d34-0410-b5e6-96231b3b80d8
-Wsentinel: Suggest nullptr in C++11 instead of NULL

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@221945 91177308-0d34-0410-b5e6-96231b3b80d8