ASan+operator new[]: Fix operator new[] cookie poisoning

Summary:
The C++ Itanium ABI says:
No cookie is required if the new operator being used is ::operator new[](size_t, void*).

We should only avoid poisoning the cookie if we're calling this
operator, not others. This is dealt with before the call to
InitializeArrayCookie.

Reviewers: rjmccall, kcc, rsmith

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D41301

llvm-svn: 321645