Libunwind.so: undefined reference to `setcontext'

Hello

I'm building the libunwind.so on X86-32.
ldd libunwind.so, it complained undefined reference to `setcontext'.
I searched with google, and found some hints on the page https://github.com/libunwind/libunwind
it says on x86, the libunwind.so requires the libc to provide the setcontext.
it seems musl libc did not provide the setcontext.

Do you know how to solve this problem?