Log Message:
gperftools: updated to 2.9.1

gperftools 2.9.1 is out!

Minor fixes landed since previous release:

* OSX builds new prefer backtrace() and have somewhat working heap
  sampling.

* Incorrect assertion failure was fixed that crashed tcmalloc if
  assertions were on and sized delete was used.

gperftools 2.9 is out!

Few more changes landed compared to rc:

* Venkatesh Srinivas has contributed thread-safety annotations
  support.

* couple more unit test bugs that caused tcmalloc_unittest to fail on
  recent clang has been fixed.

* usage of unsupportable linux_syscall_support.h has been removed from
  few places. Building with --disable-heap-checker now completely
  avoids it. Expect complete death of this header in next major
  release.