Adding clang thread safety analysis for ROS2 core packages

Next Generation ROS
13

We have two ways IMHO:

  1. Keep TSA optional and write a colcon mixin to enable this behavior.
  2. Inject the statements you quoted everywhere using the *-extras.cmake mechanism.

My feeling is that, keeping this opt-in per-package will be challenging because mixing the clang and GNU standard libraries is probably unsafe. So it would need to be a global on/off flag. 2. is most likely too brutal of a change so 1. could be the best option.