[Bug target/88952] The asm operator modifiers for rs6000 should be documented like they are for x86

[christopher.leonard at abaco dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88952

--- Comment #10 from Christopher Leonard <christopher.leonard at abaco dot com> 
---
Getting contradictory statements now:
>reg:reg+1 maps to lo:hi on x86.
>On x86, we don't allow register pairs in asm at all.

Not allowing, or printing a warning, is much better behavior than what I have
been getting on PPC.