[MemProf] Use updated version of hot/cold operator new

Switch to the just updated versions of the API in tcmalloc that change
the name of the hot cold paramter to a reserved identifier __hot_cold_t.
This was based on feedback from Richard Smith, as I also need to add
some follow-on handling to clang so they are annotated properly.

Differential Revision: https://reviews.llvm.org/D149475