[Bug target/92769] Powerpc: No way to set CR0[SO] on function return

[christophe.leroy@c-s.fr]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=92769

--- Comment #2 from Christophe Leroy <christophe.leroy@c-s.fr> ---
But CR0 being volatile doesn't prevent GCC to set/clr its SO bit just before
branching to LR as the ASM functions do, does it ?

In our ABIs, r3 is also volatile in our ABIs, it doesn't prevent using it as
function return.