5.7.0

This release includes many bug fixes, improvements to system call coverage, and incremental performance improvements. In particular, performance is improved for applications with thousands of threads (partly via the new WaitManager). A lot of rare intermittent bugs have been fixed, partly due to significant reworking of how unexpected task exits are handled.

The required Linux kernel version has been bumped to 4.7 (because we require waitid() to support __WALL). The required CMake version has been bumped to 3.5.0.

New infrastructure for building and testing rr releases in AWS EC2 instances has been constructed. This should make it easier to make more frequent and more reliable rr releases. As part of that work, we are now building Aarch64 packages.