Fixed the fmu_v5_protected build failure

platforms/common/CMakeLists.txt

@@ -51,10 +51,9 @@ add_library(px4_platform STATIC
 	px4_cli.cpp
 	shutdown.cpp
 	spi.cpp
-	Serial.cpp
 	${SRCS}
 )
-target_link_libraries(px4_platform prebuild_targets px4_work_queue px4_layer)
+target_link_libraries(px4_platform prebuild_targets px4_work_queue)
 
 if(NOT "${PX4_BOARD}" MATCHES "io-v2")
 	add_subdirectory(uORB)

platforms/nuttx/src/px4/common/px4_layer.cmake

@@ -3,6 +3,7 @@
 add_library(px4_layer
 		${KERNEL_SRCS}
 		cdc_acm_check.cpp
+		${PX4_SOURCE_DIR}/platforms/common/Serial.cpp
 		SerialImpl.cpp
 	)
 

platforms/nuttx/src/px4/common/px4_protected_layers.cmake

@@ -15,6 +15,8 @@ add_library(px4_layer
 	usr_board_ctrl.c
 	usr_hrt.cpp
 	usr_mcu_version.cpp
+	${PX4_SOURCE_DIR}/platforms/common/Serial.cpp
+	SerialImpl.cpp
 )
 
 target_link_libraries(px4_layer

platforms/posix/src/px4/common/CMakeLists.txt

@@ -46,6 +46,7 @@ add_library(px4_layer
 	drv_hrt.cpp
 	cpuload.cpp
 	print_load.cpp
+	${PX4_SOURCE_DIR}/platforms/common/Serial.cpp
 	SerialImpl.cpp
 )
 target_compile_definitions(px4_layer PRIVATE MODULE_NAME="px4")