error in building x86_freertos

I'm trying to build x86_freertos. so I run this command: scons --project=x86_freertos but I get this error:

scons: done reading SConscript files.
scons: Building targets ...
python "/home/kali/Desktop/sjtwo-c/site_scons/site_tools/unittest/unit_test_runner.py" --summary-only --timeout=5 -i "/home/kali/Desktop/sjtwo-c/_build_x86_freertos/test/test_hello_world/test_hello_world.exe"
+------------------------------+
| Unit Test Operation Summary  |
+--------------------+---------+
|        Name        |  Result |
+--------------------+---------+
|  test_hello_world  |  PASSED |
+--------------------+---------+
Linking _build_x86_freertos/x86_freertos.exe
/usr/bin/ld: _build_x86_freertos/obj/port.o: in function `pxPortInitialiseStack':
port.c:(.text+0x1a): undefined reference to `pvPortMalloc'
/usr/bin/ld: _build_x86_freertos/obj/port.o: in function `xPortStartScheduler':
port.c:(.text+0x25c): undefined reference to `vPortFree'
/usr/bin/ld: _build_x86_freertos/obj/port.o: in function `prvWaitForStart':
port.c:(.text+0x71d): undefined reference to `vPortFree'
/usr/bin/ld: _build_x86_freertos/obj/port.o: in function `prvSetupSignalsAndSchedulerPolicy':
port.c:(.text+0x9b4): undefined reference to `pvPortMalloc'
/usr/bin/ld: _build_x86_freertos/obj/event_groups.o: in function `xEventGroupCreate':
event_groups.c:(.text+0xe): undefined reference to `pvPortMalloc'
/usr/bin/ld: _build_x86_freertos/obj/event_groups.o: in function `vEventGroupDelete':
event_groups.c:(.text+0x678): undefined reference to `vPortFree'
/usr/bin/ld: _build_x86_freertos/obj/queue.o: in function `xQueueGenericCreate':
queue.c:(.text+0x173): undefined reference to `pvPortMalloc'
/usr/bin/ld: _build_x86_freertos/obj/queue.o: in function `vQueueDelete':
queue.c:(.text+0x1532): undefined reference to `vPortFree'
/usr/bin/ld: _build_x86_freertos/obj/stream_buffer.o: in function `xStreamBufferGenericCreate':
stream_buffer.c:(.text+0x90): undefined reference to `pvPortMalloc'
/usr/bin/ld: _build_x86_freertos/obj/stream_buffer.o: in function `vStreamBufferDelete':
stream_buffer.c:(.text+0x10e): undefined reference to `vPortFree'
/usr/bin/ld: _build_x86_freertos/obj/tasks.o: in function `xTaskCreate':
tasks.c:(.text+0x2e): undefined reference to `pvPortMalloc'
/usr/bin/ld: tasks.c:(.text+0x43): undefined reference to `pvPortMalloc'
/usr/bin/ld: tasks.c:(.text+0x68): undefined reference to `vPortFree'
/usr/bin/ld: _build_x86_freertos/obj/tasks.o: in function `prvDeleteTCB':
tasks.c:(.text+0x22d8): undefined reference to `vPortFree'
/usr/bin/ld: tasks.c:(.text+0x22e4): undefined reference to `vPortFree'
/usr/bin/ld: _build_x86_freertos/obj/timers.o: in function `xTimerCreate':
timers.c:(.text+0x8e): undefined reference to `pvPortMalloc'
/usr/bin/ld: _build_x86_freertos/obj/timers.o: in function `prvProcessReceivedCommands':
timers.c:(.text+0x883): undefined reference to `vPortFree'
collect2: error: ld returned 1 exit status
scons: *** [_build_x86_freertos/x86_freertos.exe] Error 1
scons: building terminated because of errors.