Nicholas Piggin via Libc-alpha [off-list ref] writes:

As a more hacky thing you could make a syscall with -1 and see how
the error looks, and then assume all syscalls will be the same.

I'm not sure this would work.
Even in glibc, it's expected that early syscalls will use sc while scv is used
later in the execution.

-- 
Tulio Magno