[Bug target/91050] -mdejagnu-cpu=<cpu> does not affect the -m<cpu> assembler option

[bergner at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91050

--- Comment #10 from Peter Bergner <bergner at gcc dot gnu.org> ---
(In reply to Alan Modra from comment #8)
> Created attachment 46555 [details]
> assembler command line fixes
> 
> I'll happily handle the assembler command line problems.  Here's a lightly
> tested patch.

This fixes the issue Anton was seeing (mentioned offline), correct?  So not
related to -mdejagnu-cpu=... not affecting the -m<cpu> assembler option?  At
least I don;t see how your patches could fix that without touching asm_cpu
spec.  That bug I know how to fix, but it doubles the size of that table
because *all* -mdejagnu-cpu entries in that table have to be able to override
all of the -mcpu entries and I'd like to see that table be smaller rather than
double in size, so I'm trying to think of a different way to fix it.  Ideas
welcome! :-)  Maybe it would help to have a rs6000_rewrite_cpu function like
arm and aarch64 have?