fork() on Linux/sparc64 seems to return its result in two registers,
with %o0 always holding the current process' PID, and the parent/child
status returned in %o1. Add some glue code to convert those into
the libc-style return value.
There's no guarantee for the kernel definition to be ABI compatible with
the libc one (and vice versa).
There's also no guarantee of ABI compatibility between musl/glibc.
Fun, isn't it?
Koakuma