Don't compile some opcodes files when bfd is 32-bit only

[Alan Modra]

On Thu, Dec 09, 2021 at 02:05:54PM -0800, Jim Wilson wrote:
> On Thu, Dec 2, 2021 at 2:02 PM Alan Modra via Binutils <
> binutils@sourceware.org> wrote:
> 
> > Reverting the opcodes Makefile changes will currently result in
> > opcodes failing to link.  The riscv opcodes objects now depend on
> > riscv bfd objects that are only compiled for a 64-bit bfd.
> >
> 
> Nelson Chu submitted a patch Nov 12 to fix 32-bit riscv32 builds, but at
> the time the patch didn't seem necessary.  I think this should be
> revisited.  I think this patch would fix some of these issues people are
> having with 32-bit enable-targets=all builds.
> https://sourceware.org/pipermail/binutils/2021-November/118498.html

I am of course fine with a patch that makes it possible for a 32-bit
objdump to disassemble riscv object files.  What I'd like to avoid is
compiling useless code into libopcodes.  It's not just a matter of
being able to build binutils/sim but also for bfd to recognise and
opcodes to disassemble the target object files.  (I haven't tried out
Nelson's patch, this is a general comment not one specific to the
patch.)

-- 
Alan Modra
Australia Development Lab, IBM