[Bug target/98519] rs6000: @pcrel unsupported on this instruction error in pveclib

[bergner at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98519

--- Comment #31 from Peter Bergner <bergner at gcc dot gnu.org> ---
(In reply to Segher Boessenkool from comment #30)
> We have to disallow all (*all*) operands that require prefixed insns, until
> we can handle those properly.

So if we can't disallow pcrel addresses in asm operands in 
rs6000_legitimate_address_p, then where can we disallow them when they're used
with all of the current memory constraints?  Ie, not the new pcrel address
friendly constraint we don't have yet?