initial minimal PX4_ROS2 platform and px4_ros2_default build (#20689)

- new ROS2 platform in PX4 intended for creating configs that build and run entirely in ROS2
 - PX4_CONFIG defaults to px4_ros2_default if no config specified and in a colcon workspace with ROS_VERSION=2
 - currently doesn't do much other than allow you to build px4 msgs interface package

platforms/common/CMakeLists.txt

@@ -40,7 +40,7 @@ if(NOT "${PX4_PLATFORM}" MATCHES "qurt" AND NOT "${PX4_BOARD}" MATCHES "io-v2" A
 	)
 endif()
 
-add_library(px4_platform
+add_library(px4_platform STATIC
 	board_common.c
 	board_identity.c
 	events.cpp
@@ -56,7 +56,7 @@ add_library(px4_platform
 )
 target_link_libraries(px4_platform prebuild_targets px4_work_queue)
 
-if (NOT "${PX4_BOARD}" MATCHES "io-v2")
+if(NOT "${PX4_BOARD}" MATCHES "io-v2")
 	add_subdirectory(uORB)
 endif()
 

platforms/common/include/px4_platform_common/tasks.h

@@ -67,7 +67,7 @@ typedef int px4_task_t;
 /** Default scheduler type */
 #define SCHED_DEFAULT	SCHED_FIFO
 
-#if defined(__PX4_LINUX) || defined(__PX4_DARWIN) || defined(__PX4_CYGWIN)
+#if defined(__PX4_LINUX) || defined(__PX4_DARWIN) || defined(__PX4_CYGWIN) || defined(__PX4_ROS2)
 
 #define SCHED_PRIORITY_MAX sched_get_priority_max(SCHED_FIFO)
 #define SCHED_PRIORITY_MIN sched_get_priority_min(SCHED_FIFO)

platforms/common/work_queue/CMakeLists.txt

@@ -32,9 +32,9 @@
 ############################################################################
 
 # nuttx uses internal work queue currently
-if (NOT "${PX4_PLATFORM}" MATCHES "nuttx")
+if(NOT "${PX4_PLATFORM}" MATCHES "nuttx")
 
-	add_library(work_queue
+	add_library(work_queue STATIC
 		dq_addlast.c
 		dq_rem.c
 		dq_remfirst.c

platforms/common/work_queue/work_lock.c

@@ -35,6 +35,7 @@
 #include <stdio.h>
 #include "work_lock.h"
 
+#include <px4_platform_common/sem.h>
 
 extern px4_sem_t _work_lock[];