[Bug target/104189] enable 64-bit compare-and-swap on SPARC/Linux with V9

[ebotcazou at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104189

--- Comment #2 from Eric Botcazou <ebotcazou at gcc dot gnu.org> ---
Created attachment 52272
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=52272&action=edit
Tentative fix

This requires that the kernel preserves the full 64-bit registers even in
32-bit mode, like on Solaris.