[seL4] Does sel4 support pthread?

I am using sel4 to develop a multi-thread program on ARM platform. I know that sel4 support musl libc. But when I call __pthread_create the program returns an error. Does sel4 support pthread on ARM platform? By the way, I get the libmuslc from seL4test. So if there is a musl libc which has pthread inside that can be used by sel4, please tell me where I can get it. Thank you.