[Bug target/79179] PowerPC64: -mcpu=power9 creates stxsd with bad offset

[meissner at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79179

--- Comment #1 from Michael Meissner <meissner at gcc dot gnu.org> ---
Created attachment 40584
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=40584&action=edit
Proposed patch to fix the problem.