Preserve PLT flag in copy_indirect

[Bob Wilson]

Alan Modra wrote:
> Also, what about all the backend copy_indirect functions?  I think the
> patch should also adjust them for consistency.

The Xtensa copy_indirect function can be removed entirely.  It only exists 
because the default copy_indirect function was not preserving the PLT flag. 
Feel free to remove the Xtensa function as part of your patch, Daniel. 
Otherwise, I'll do it after your patch goes in.

--Bob