Issue a warning if a throwing operator new or operator new[] returns a null
pointer, since this invokes undefined behavior. Based on a patch by Artyom
Skrobov! Handling of dependent exception specifications and some additional
testcases by me.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@199452 91177308-0d34-0410-b5e6-96231b3b80d8