dynamic_annotations symbols in the global namespace

Abseil dynamic_annotations (https://github.com/abseil/abseil-cpp/blob/master/absl/base/dynamic_annotations.h, https://github.com/abseil/abseil-cpp/blob/master/absl/base/dynamic_annotations.cc) define macros and functions without ABSL_ or Absl prefix (this is C code, so we cannot use namespaces).

This behavior can cause ODR violations and macros clashing. A possible solution would be to prefix all the macros with ABSL_ and all the functions with Absl. This will make Abseil compatible also with projects that are using something like https://code.google.com/archive/p/data-race-test/wikis/DynamicAnnotations.wiki.