[Bug target/66474] Document the use of %x in powerpc asm statements

[meissner at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66474

--- Comment #1 from Michael Meissner <meissner at gcc dot gnu.org> ---
Created attachment 35732
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=35732&action=edit
Proposed patch to fix the problem