[jhanca-robotecai]

What does this PR do?

With ROS 2 Lyrical, processes that unload the ROS2 gem crash with SIGSEGV during process exit. The cause is in ROS 2: rmw_implementation and rcl_logging_implementation unload their plugin libraries (librmw_fastrtps_cpp, librcl_logging_spdlog) during process exit, from a static destructor and an atexit() handler. When the ROS2 gem has been unloaded before, that plugin can be the last reference keeping the ROS 2 libraries loaded, so its unload also unmaps librmw_implementation / librcl_logging_implementation while their code is still running.

This PR makes ROS2SystemComponent::Init() mark the already loaded librclcpp.so as non-unloadable (dlopen(..., RTLD_NOLOAD | RTLD_NODELETE)), right before rclcpp::init(). rclcpp and everything it depends on, including both libraries above, then stay loaded until the process ends, so the exit-time unloads cannot unmap code that is still running. RTLD_NOLOAD only changes the flags of the library that is already loaded; nothing new is loaded. The ROS2 gem is Linux-only, so dlfcn.h is available.

How was this PR tested?

Ubuntu 26.04, ROS 2 Lyrical, clang 21, profile build of a project with the o3de-extras ROS 2 gems, engine 2705 (development based): tests pass with the fix;SimulationInterfaces.ROS2Tests with the dlopen call suppressed (LD_PRELOAD interposer): exit code 139 without.

[jhanca-robotecai]

Tests fail due to: #1106
Btw. CI in this repo tests only ROS 2 Humble.

[michalpelka]

I would suggest:

• add issues pointer (ROS2 repo) to source code - to remove it on some point.
• assert return value, just in case (e.g. someone has a great idea to change librclcpp.so to smth else ).

[jhanca-robotecai]

Rebased on top of #1106 to ensure the tests pass.