Log Message:
gperftools: updated to 2.8.1

gperftools-2.8.1 is out!

Here are notable changes:

previous release contained change to release memory without page heap lock, but \ 
this change had at least one bug that caused to crashes and corruption when \ 
running under aggressive decommit mode (this is not default). While we check for \ 
other bugs, this feature was reverted.

stack traces depth captured by gperftools is now up to 254 levels deep. Thanks \ 
to Kerrick Staley for this small but useful tweak.

Levon Ter-Grigoryan has contributed small fix for compiler warning.

Grant Henke has contributed updated detection of program counter register for OS \ 
X on arm64.

Tim Gates has contributed small typo fix.

Steve Langasek has contributed basic build fixes for riscv64.

Isaac Hier and okhowang have contributed premiliminary port of build \ 
infrastructure to cmake. This works, but it is very premiliminary. \ 
Autotools-based build is the only officially supported build for now.