[codeview] Put !heapallocsite on calls to operator new

Clang marks calls to operator new as heap allocation sites, but the
operator declared at global scope returns a void pointer. There is no
explicit cast in the code, so the compiler has to write down the
allocated type itself.

Also generalize a cast to use CallBase, so that we mark heap alloc sites
when exceptions are enabled.

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D80966