[musl] Powerpc Linux 'scv' system call ABI proposal take 2

[Nicholas Piggin]

Excerpts from Szabolcs Nagy's message of April 16, 2020 7:58 pm:
> * Nicholas Piggin via Libc-alpha <libc-alpha@sourceware.org> [2020-04-16 10:16:54 +1000]:
>> Well it would have to test HWCAP and patch in or branch to two 
>> completely different sequences including register save/restores yes.
>> You could have the same asm and matching clobbers to put the sequence
>> inline and then you could patch the one sc/scv instruction I suppose.
> 
> how would that 'patch' work?
> 
> there are many reasons why you don't
> want libc to write its .text

I guess I don't know what I'm talking about when it comes to libraries. 
Shame if there is no good way to load-time patch libc. It's orthogonal
to the scv selection though -- if you don't patch you have to 
conditional or indirect branch however you implement it.

Thanks,
Nick