heap_profiler: support new gperftools header locations

This is tracked in Redmine at http://tracker.ceph.com/issues/10231

The `google/` headers location has been deprecated as of gperftools 2.0. As of gperftools 2.2rc, the `google/` headers will now give deprecation warnings, and they will probably disappear in a future gperftools update.

An original fix for this was proposed at https://github.com/ceph/ceph/pull/2267 , but that was not backwards-compatible with older gperftools releases (eg. Ubuntu 12.04 Precise). The fix in this pull request should be fully forwards- and backwards-compatible.

CC'ing @branto1 in case he wants to review.