PATCH bfd: Fix linker warning for recently introduced arm attributes

[Nick Clifton]

Hi Andrea,

> this simple patch updates the value of 'NUM_KNOWN_OBJ_ATTRIBUTES' so
> that when linking objects with 'Tag_BTI_use' or 'Tag_PACRET_use' set ld
> does not emit the "unknown EABI object attribute" warning.
> 
> Regtested clean, okay for trunk?

Approved - please apply.

Cheers
   Nick