PX4 ROS2 msg conformity and explicit topics

- .msg files are PascalCase
 - topics are still either per msg or explicitly listed in TOPICS
 - compatible structs are still generated (eg struct msg_s), but ROS2 style px4::msg::Msg is also available

platforms/nuttx/cmake/px4_impl_os.cmake

@@ -64,10 +64,19 @@ function(px4_os_add_flags)
 		${PX4_SOURCE_DIR}/platforms/nuttx/NuttX/apps/include
 	)
 
-	# prevent using the toolchain's std c++ library
-	add_compile_options($<$<COMPILE_LANGUAGE:CXX>:-nostdinc++>)
 
-	add_compile_options($<$<COMPILE_LANGUAGE:CXX>:-fno-sized-deallocation>)
+	set(cxx_flags)
+	list(APPEND cxx_flags
+		-fno-exceptions
+		-fno-rtti
+		-fno-sized-deallocation
+		-fno-threadsafe-statics
+		-nostdinc++ # prevent using the toolchain's std c++ library
+	)
+
+	foreach(flag ${cxx_flags})
+		add_compile_options($<$<COMPILE_LANGUAGE:CXX>:${flag}>)
+	endforeach()
 
 	add_definitions(
 		-D__PX4_NUTTX