- use NuttX gdb script for nxthreads and thread backtrace
- update jlink_gdb_backtrace and jlink_debug_gdb helper targets to use
NuttX gdb script
- Debug/PX4 fix "perf" divide by zero
- Debug/PX4 add "dmesg"
- cmake NuttX build wrapper compile in place instead of copying source tree to build directory
- slightly faster skipping necessary copying (depending on system)
- allows debugging in place
- easier to work directly in NuttX following official documentation
- simplifies overall build which should make it easier to resolve any remaining NuttX dependency issues in the build system
- the downside is switching back and forth between different builds always require rebuilding NuttX, but I think this is worth the improved developer experience
- also no longer builds px4io and bootloader in every single build, for most users these rarely change and we're wasting a lot of build time