RFC: Add AIX .ref support

[Nick Clifton]

Hi Richard,

> Tested on powerpc-ibm-aix6.1.

Please run a regression test with an x86 or x86_64 toolchain, just to be 
sure.  Assuming that that passes OK then:

> bfd/
> 	* coff-rs6000.c (xcoff_howto_table): Change size to 0 and bitsize to 1.
> 	(_bfd_xcoff_reloc_type_lookup): Handle BFD_RELOC_NONE.
> 	* coff64-rs6000.c (xcoff64_howto_table): Change size to 0 and
> 	bitsize to 1.
> 	(xcoff64_reloc_type_lookup): Handle BFD_RELOC_NONE.
>
> gas/
> 	* write.h (fix_at_start): Declare.
> 	* write.c (fix_new_internal): Add at_beginning parameter.
> 	Use it instead of REVERSE_SORT_RELOCS.  Fix the handling of
> 	seg_fix_tailP for the at_beginning/REVERSE_SORT_RELOCS case.
> 	(fix_new, fix_new_exp): Update accordingly.
> 	(fix_at_start): New function.
> 	* config/tc-ppc.c (md_pseudo_table): Add .ref to the OBJ_XCOFF section.
> 	(ppc_ref): New function, for OBJ_XCOFF.
> 	(md_apply_fix): Handle BFD_RELOC_NONE for OBJ_XCOFF.
> 	* config/te-i386aix.h (REVERSE_SORT_RELOCS): Remove #undef.
>
> gas/testsuite/
> 	* gas/ppc/xcoff-ref-1.s, gas/ppc/xcoff-ref-1.l: New test.
> 	* gas/ppc/aix.exp: Run it.
>
>
> ld/testsuite/
> 	* ld-powerpc/aix-ref-1-32.od, ld-powerpc/aix-ref-1-64.od,
> 	ld-powerpc/aix-ref-1.s: New tests.
> 	* ld-powerpc/aix52.exp: Run them.

Approved - please apply.

Cheers
   Nick