[MemProf] Recognize hot/cold operator new as replaceable allocations

Follow up to LLVM-side change to allow conversion to hot/cold hinted
operator new, not yet standard but supported by open source tcmalloc.
The LLVM change in a35206d7 added the
necessary support to recognize these as library functions, and we
subsequently found that a clang-side change is needed to give them
builtin/nobuiltin attributes as appropriate so they have consistent
removeability.

Based on discussion with Richard Smith, converted the parameter type to
a reserved identifier (39f7b486) and
added support in this patch to recognize it in clang.

Differential Revision: https://reviews.llvm.org/D149600