Remove plugin target setting entirely from binutils/

[Alan Modra]

On Mon, Aug 18, 2025 at 07:48:46PM +0930, Alan Modra wrote:
> This is what I had in mind.  It has been tested by building my usual
> list of 162 binutils target triples, some with cross-compilers
> installed, without finding any regressions.  So, lightly tested.

Pushed with a small change, removing the !bfd_plugin_target_p check in
the new check_format code and replacing it with an assert.

> I'll also add a NEWS entry

* Internal changes to plugin support, and stricter target checking may result
  in some errors being exposed in user options passed to the various binutils.
  For example objcopy --target=TARGET now will only work if the input file is
  for TARGET whereas prior versions of objcopy accepted other target input
  files and produced a TARGET output.  If you do in fact want the old
  behaviour the correct usage is objcopy --output-target=TARGET.

-- 
Alan Modra