fix for nick's latest patch

[Nick Clifton]

Hi Alan,

> Nick's latest patch missed a couple of places.  So if you build with
> --enable-targets=all or otherwise happen to pull in xcoff support,
> bad things happen.
> 
> 	* coff-rs6000.c (rs6000coff_vec): Add initializer for
> 	bfd_is_target_special_symbol.
> 	* coff64-rs6000.c (rs6000coff64_vec): Likewise.
> 	* som.c (som_bfd_is_target_special_symbol): Define.

Doh!  It is surprising though because I did build with 
--enable-targets=all and also with that and --enable-64-bit-bfd and 
there were no build failures in either case.  Strange...

Cheers
   Nick