cmake improve ROMFS dependencies for px4io inclusion (#8860)

- fixes #8858

ROMFS/CMakeLists.txt

@@ -28,19 +28,29 @@ list(APPEND romfs_dependencies
 	${romfs_temp_dir}/init.d/rc.autostart
 	)
 	
-# create romfs.bin
+# copy px4io binary if configured
+if (config_io_board)
+	list(APPEND romfs_dependencies
+		copy_px4io_bin
+		${fw_io_bin}
+		)
+endif()
+
+# create romfs.img
 add_custom_command(OUTPUT romfs.img
+	COMMAND ${CMAKE_COMMAND} -E remove -f romfs.img romfs.txt
 	COMMAND ${GENROMFS} -f romfs.img -d ${romfs_temp_dir} -V "NSHInitVol" -v > romfs.txt 2>&1
 	DEPENDS ${romfs_dependencies}
 	)
 
-# create romfs.o
+# create nsh_romfsimg.c
 add_custom_command(OUTPUT nsh_romfsimg.c
+	COMMAND ${CMAKE_COMMAND} -E remove -f nsh_romfsimg.c
 	COMMAND xxd -i romfs.img nsh_romfsimg.c
 	COMMAND sed 's/unsigned/const unsigned/g' nsh_romfsimg.c > nsh_romfsimg.c.tmp && mv nsh_romfsimg.c.tmp nsh_romfsimg.c
 	DEPENDS romfs.img
 	)
 
 add_library(romfs STATIC nsh_romfsimg.c)
-add_dependencies(romfs platforms__common)
+add_dependencies(romfs prebuild_targets)
 set_target_properties(romfs PROPERTIES LINKER_LANGUAGE C)

platforms/nuttx/CMakeLists.txt

@@ -94,9 +94,6 @@ target_link_libraries(${FW_NAME}
 if (config_romfs_root)
 	add_subdirectory(${PX4_SOURCE_DIR}/ROMFS ${PX4_BINARY_DIR}/ROMFS)
 	target_link_libraries(${FW_NAME} romfs)
-	if (config_io_board)
-		add_dependencies(romfs copy_px4io_bin)
-	endif()
 endif()
 
 # create px4 file (combined firmware and metadata)

src/drivers/px4io/CMakeLists.txt

@@ -65,6 +65,7 @@ add_custom_command(OUTPUT ${fw_io_exe}
 
 file(RELATIVE_PATH fw_io_exe_relative ${CMAKE_CURRENT_BINARY_DIR} ${fw_io_exe})
 file(RELATIVE_PATH fw_io_bin_relative ${CMAKE_CURRENT_BINARY_DIR} ${fw_io_bin})
+set(fw_io_bin ${fw_io_bin} PARENT_SCOPE)
 
 add_custom_command(OUTPUT ${fw_io_bin}
 	COMMAND mkdir -p ${PX4_BINARY_DIR}/ROMFS/${config_romfs_root}/extras/