Blender Git Loki

Guardedalloc: Implement atomic peak memory update

Updating maximum requires a bit of a cycle which usually does 1 iteration only,
sometimes needs a bit more but seems there's no speed regressions.

For now the code is commented out. This way it's easier for others to verify
there's no speed regressions.

Reviewers: campbellbarton

Differential Revision: https://developer.blender.org/D626