[Bug target/91886] [10 regression] powerpc64 impossible constraint in asm

[bugdal at aerifal dot cx]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91886

--- Comment #14 from Rich Felker <bugdal at aerifal dot cx> ---
> So, if "ws" has been documented in the user documentation, perhaps just
> (define_register_constraint "ws" "rs6000_constraints[RS6000_CONSTRAINT_wa]"
>   "Compatibility alias to wa")
> could be added?  If it has not been documented, it is fine to remove it.

It is clearly documented here:

https://gcc.gnu.org/onlinedocs/gcc-9.2.0/gcc/Machine-Constraints.html

Whoever removed it in gcc 10 was aware of this because they explicitly deleted
it from the documentation:

https://gcc.gnu.org/onlinedocs/gcc/Machine-Constraints.html

This should not be a permitted change, at least not without major discussion to
reach consensus.