[Sanitizers] Operator new() interceptors always die on allocation error

Summary:
Operator new interceptors behavior is now controlled by their nothrow
property as well as by allocator_may_return_null flag value:

- allocator_may_return_null=* + new()        - die on allocation error
- allocator_may_return_null=0 + new(nothrow) - die on allocation error
- allocator_may_return_null=1 + new(nothrow) - return null

Ideally new() should throw std::bad_alloc exception, but that is not
trivial to achieve, hence TODO.

Reviewers: eugenis

Subscribers: kubamracek, llvm-commits

Differential Revision: https://reviews.llvm.org/D34731

llvm-svn: 306604