ROMFS/CMakeLists.txt: change dependencies

- moves process airframe deps to the tar generation, to ensure whenever
  airframes are processed, the tar is extracted first.
  This is required, because if the airframe processing is done on pruned
  ROMFS, it's missing the tags.
- avoid using init.d/rcS in dependencies, use a separate file instead.
  This is because pruning modifies the rcS, and the next rebuild was
  seeing a changed rcS, resulting in unnecessary regeneration.

ROMFS/CMakeLists.txt

@@ -95,11 +95,24 @@ add_custom_command(
 	OUTPUT ${romfs_tar_file}
 	COMMAND ${CMAKE_COMMAND} -E tar cf ${romfs_tar_file} ${romfs_copy_files_relative}
 	WORKING_DIRECTORY ${romfs_src_dir}
-	DEPENDS ${romfs_copy_files}
+	DEPENDS
+		${romfs_copy_files}
+		${jinja_templates}
+		${module_config_files}
+		${romfs_cmake_files}
+		${PX4_SOURCE_DIR}/Tools/px_process_airframes.py
+		${PX4_SOURCE_DIR}/Tools/px4airframes/markdownout.py
+		${PX4_SOURCE_DIR}/Tools/px4airframes/rcout.py
+		${PX4_SOURCE_DIR}/Tools/px4airframes/srcparser.py
+		${PX4_SOURCE_DIR}/Tools/px4airframes/srcscanner.py
+		${PX4_SOURCE_DIR}/Tools/px4airframes/xmlout.py
+		${PX4_SOURCE_DIR}/Tools/serial/generate_config.py
 	)
+set(romfs_extract_stamp ${CMAKE_CURRENT_BINARY_DIR}/romfs_extract.stamp)
 add_custom_command(
-	OUTPUT ${romfs_gen_root_dir}/init.d/rcS
+	OUTPUT ${romfs_extract_stamp}
 	COMMAND ${CMAKE_COMMAND} -E tar xf ${romfs_tar_file}
+	COMMAND ${CMAKE_COMMAND} -E touch ${romfs_extract_stamp}
 	WORKING_DIRECTORY ${romfs_gen_root_dir}
 	DEPENDS ${romfs_tar_file}
 	)
@@ -120,17 +133,7 @@ add_custom_command(
 		--config-files ${module_config_files} #--verbose
 	COMMAND ${CMAKE_COMMAND} -E touch romfs_copy.stamp
 	DEPENDS
-		${romfs_gen_root_dir}/init.d/rcS
-		${jinja_templates}
-		${module_config_files}
-		${romfs_cmake_files}
-		${PX4_SOURCE_DIR}/Tools/px_process_airframes.py
-		${PX4_SOURCE_DIR}/Tools/px4airframes/markdownout.py
-		${PX4_SOURCE_DIR}/Tools/px4airframes/rcout.py
-		${PX4_SOURCE_DIR}/Tools/px4airframes/srcparser.py
-		${PX4_SOURCE_DIR}/Tools/px4airframes/srcscanner.py
-		${PX4_SOURCE_DIR}/Tools/px4airframes/xmlout.py
-		${PX4_SOURCE_DIR}/Tools/serial/generate_config.py
+		${romfs_extract_stamp}
 	COMMENT "ROMFS: copying, generating airframes"
 	)
 
@@ -208,7 +211,7 @@ add_custom_command(OUTPUT romfs_extras.stamp
 
 add_custom_target(romfs_gen_files_target
 	DEPENDS
-		${romfs_gen_root_dir}/init.d/rcS
+		${romfs_extract_stamp}
 		${romfs_gen_root_dir}/init.d/rc.serial
 		romfs_extras.stamp
 	)