Log Message:
abseil: updated to 20200923.2

Abseil LTS 20200923, Patch 2

What's New:

absl::StatusOr<T> has been released. See our blog
post for more information.
Abseil Flags reflection interfaces have been released.
Abseil Flags memory usage has been significantly optimized.
Abseil now supports a "hardened" build mode. This build mode enables
runtime checks that guard against programming errors that may lead
to security vulnerabilities.

Notable Fixes:

Sanitizer dynamic annotations like AnnotateRWLockCreate that are
also defined by the compiler sanitizer implementation are no longer
also defined by Abseil.
Sanitizer macros are now prefixed with ABSL_ to avoid naming collisions.
Sanitizer usage is now automatically detected and no longer requires
macros like ADDRESS_SANITIZER to be defined on the command line.

Breaking Changes:

Abseil no longer contains a dynamic_annotations library. Users
using a supported build system (Bazel or CMake) are unaffected by
this, but users manually specifying link libraries may get an error
about a missing linker input.